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Radiation Safety

Analytical X-Ray Safety Manual

1.0  Radiation Safety Program

Introduction

Analytical x-ray equipment generates high intensity ionizing radiation. Improper or careless use of this equipment can cause severe and permanent injury if any part of the body is exposed to the primary beam even for a few seconds.

Productive programs of teaching and research should encourage the safe use of radioactive materials and devices that generate radiation. This can be accomplished through education and the application of sound radiation safety principles that minimize exposure. The purpose of this manual is to ensure that analytical x-ray equipment is used safely at Radford University without imposing undue restrictions on the use of the equipment.

The manual is divided into two sections. Part I describes the radiation safety program and the rules and regulations for the safe use of analytical x-ray equipment. These requirements are in conformity with the radiation safety standards established by the Commonwealth of Virginia and the American National Standards Institute (ANSI).

Part II contains training material describing the general properties of ionizing radiation, radiation detection equipment, personnel monitoring devices, biological effects, radiation hazards, and procedures to minimize exposure.

Radiation Safety Committee

The Radiation Safety Committee has been established by the University with the authority to regulate the safe use of radioisotopes, x-ray equipment, and non-ionizing radiation. The Radiation Safety Committee shall perform the following functions:

  1. Review and interpret Federal and State regulations, develop University regulations and oversee their implementation.
  2. Approve all applications for the use of radioisotopes and x-ray equipment and monitor the operation of the facilities and users.
  3. Approve "new experiments" which differ in size, kind, and/or scope from previous experiments.
  4. Review violations for failure to comply with regulations developed by the committee.

Members of the committee are appointed by the Chair of the Radiation Safety Committee. They are selected on the basis of their experience in the safe handling of radioactive materials, x-ray equipment, or non-ionizing radiation. An individual with administrative responsibilities shall chair the committee. The Radiation Safety Officer is an ex-officio member of the committee. At least one user of radioisotopes and one analytical x-ray user will serve on the committee. Additional members as deemed necessary may be approved by the Chair. Members will serve for three years and may be re-appointed upon completion of their terms. A member who misses three consecutive meetings without approval of the Chair will be considered to have resigned.

A meeting of the committee will be held at least quarterly. Additional meetings will be convened by the Chair as necessary. Minutes of the meetings shall be recorded and distributed to the members of the committee and other interested persons. A quorum shall consist of half the members plus one. The Chair and the Radiation Safety Officer have the authority to act on behalf of the committee for those occasions that do not warrant a special meeting of the full committee (e.g., approval of an amendment).

Decisions of the full committee are effective immediately. Decisions made at interim meetings are tentative, pending approval by the full committee. A member may request a review by the Radiation Safety Committee if a decision is not unanimous. The decision shall not be implemented pending this review.

Radiation Safety Officer

The Radiation Safety Officer (RSO) will supervise the University's Health Physics Program and advise others in the safe use of ionizing and non-ionizing radiation. The RSO will perform the following duties:

  1. Act in a supervisory capacity in all aspects of the University's radiation measurement and protection activities, including responsibility for personnel monitoring, maintenance of exposure records, survey methods, survey meters, waste disposal and regulations, and radiological safety practices as specified by NRC regulations, the Commonwealth of Virginia, or as approved by the Radiation Safety Committee.
  2. Provide written approval for all activities and procedures which involve actual or potential exposure of personnel to radiation. The RSO will bring those activities not covered by established procedures to the Radiation Safety Committee.
  3. Provide advice in radiological safety practices to all users of ionizing and non-ionizing radiation.
  4. Suspend any operation as rapidly as possible that is causing or may cause an excessive radiation hazard. The RSO will promptly notify the Radiation Safety Committee which will review the incident.
  5. Perform routine and special radiation surveys as deemed necessary in the interest of radiation safety.
  6. Prepare a quarterly report of incidents, materials received, and an inventory of radioactive material and x-ray equipment on campus for the Radiation Safety Committee.
  7. Maintain a current list of authorized users of radioisotopes and x-ray equipment, indicating any additions or deletions, and provide a copy of this list to members of the Radiation Safety Committee. 

Personnel Requirements

Classification of Users

Authorized User - An authorized user may independently purchase, possess, and use x-ray equipment. The authorized user is directly responsible for the equipment and the users on the authorization. Authorized users must be approved by the Department Head.

Principal User - A principal user works under the indirect supervision of an authorized user and may supervise other workers and request amendments to the authorization. Principal users are typically professors appointed by the authorized user to supervise experiments.

General User - A general user works with x-ray equipment under the indirect supervision of an authorized or principal user. General users have no supervisory authority and may not request amendments. General users may be professors, technicians, or students doing independent research.

Student User - A student user works with the equipment only as part of a classroom requirement approved by the Radiation Safety Committee. Student users must be under the direct supervision of an authorized or principal user.

Authorized Users

Authorized users are responsible for the safe operation of x-ray equipment under their control. Authorized users will ensure that:

  1. Users are adequately instructed in safe operating procedure and skilled in the safe use of the equipment.
  2. Users have received training in radiation safety principles as considered necessary by the Radiation Safety Committee.
  3. Written safety rules and procedures are provided to all users of the equipment.
  4. All x-ray equipment under their control are registered with the Safety Office.
  5. Equipment, facilities, and use of the equipment meets all applicable federal, state, and local regulations.
  6. Users wear the appropriate personnel monitoring devices.
  7. The Safety Office is notified of any changes in the equipment, facilities, or personnel using the equipment.

Responsibility of Users

Individuals who work with analytical x-ray equipment shall:

  1. Follow safe operating procedures for the use of the equipment.
  2. Observe the radiation safety rules presented in this manual for the use of analytical x-ray equipment.
  3. Immediately notify the authorized user or the RSO of any defects or deficiencies in radiation protection devices and procedures.
  4. Wear the appropriate personnel monitoring device.
  5. Know what to do in the event of a radiation emergency.
  6. Maintain radiation doses at a level that is low as reasonably achievable (ALARA).


Obtaining An Authorization

An individual wishing to become an authorized user must submit an application form to the Radiation Safety Officer. The application will be submitted to the Radiation Safety Committee for review. The applicant will be notified within two weeks as to whether the application has been approved. A copy of the approved form will be sent to the applicant's department head. Before an application can be approved, the applicant must pass the radiation safety exam or be granted an exemption by the Radiation Safety Committee.

Obtaining X-Ray Equipment

Only authorized users can possess x-ray equipment. The authorized user must consult with the Radiation Safety Officer prior to obtaining the equipment to ensure that the facility is adequate and the equipment meets state requirements. The purchase order must be approved by the Radiation Safety Officer. The authorized user must notify the RSO when the equipment arrives and provide the necessary information to register the unit with the state. The RSO will conduct a leakage and area survey during the initial operation of the equipment.

Radiation Safety Training

Users of analytical x-ray equipment must receive training and demonstrate competence in radiation safety principles. Authorized and principal users shall receive training in the following:

  • General properties of ionizing radiation.
  • Principles of radiation detection.
  • Radiation hazards associated with the use of the equipment.
  • Biological effects of ionizing radiation.
  • Procedures to minimize exposure.
  • Radiation safety regulations for the equipment.
  • Emergency procedures.
  • Proper operating procedures for the equipment.
  • Purposes and functions of the radiation warning and safety devices.
  • Radford's Radiation Safety Program.

Authorized users should determine the extent of training necessary for users under their control, based on the intended use of the equipment and degree of supervision. As a minimum, general and student users must receive training in:

  • Radiation hazards associated with the use of the equipment.
  • Biological effects of ionizing radiation.
  • Procedures to minimize exposure.
  • Emergency procedures.
  • Proper operating procedures for the equipment.
  • Purposes and functions of the radiation warning and safety devices.

General and student users who will be monitoring analytical x-ray equipment and/or wearing personnel monitoring devices should also read the appropriate sections in chapter 5.

Competence will usually be demonstrated by passing a written examination administered by the Radiation Safety Officer. Exceptions to taking the examination may be granted by the Radiation Safety Committee because of previous training, experience, or education. Individuals wishing to seek an exemption should submit a request in writing to the RSO or the Chair of the Radiation Safety Committee.

Students using x-ray equipment as part of a classroom requirement under the direct supervision (in the room) of an authorized or principal user are not required to take the radiation safety test. Students under direct supervision should sign a training acknowledgement form.

Individuals who need training in radiation safety principles should call the Radiation Safety Officer at 831-5860 to obtain a copy of the Analytical X-Ray Safety Manual. A test will be scheduled after the user has reviewed the applicable sections of the training manual. A personnel monitoring device will be ordered, if necessary, after the individual has passed the test. The equipment cannot be used until the monitoring device has been issued.

An amendment to the authorization signed by the authorized or principal user must be submitted to the RSO prior to use of the equipment.

Classroom Instruction

Prior to the start of the class, a basic protocol listing the equipment, student roster, and the intended use must be submitted to the RSO for approval. If personnel monitoring devices are required, social security numbers and birth dates should also be submitted.

Students must receive training in basic radiation safety principles and wear personnel monitoring devices, if required, before the equipment can be operated.

Request For Inspection

Any user who believes there has been a violation of the rules presented in this manual may request an inspection by notifying the Safety Office at Radford University or the State Bureau of Radiological Health. The user's name will be kept anonymous. During the inspection, safety representatives may confer privately with users. Users may bring to the attention of safety representatives any past or present condition they believe may have contributed to or caused a violation. An authorized user shall not dismiss or discriminate against a user because a complaint was filed. The RSO will bring any complaints to the attention of the Radiation Safety Committee.

Variance

An authorized user may apply to the Radiation Safety Committee for an exemption from these regulations. In addition to including the reason the variance is being sought, the application must include alternative methods that will be employed to ensure that the health and safety of personnel and the environment will not be compromised.

The application for a variance shall be sent to the RSO or the Chair of the Radiation Safety Committee. The request will normally be acted upon at the next regular scheduled meeting of the Committee. A special meeting may be called by the Chair if deemed necessary. The authorized user may be present at the meeting to discuss his/her request for the variance.

Radiation Protection

Exposure Limits

1. Radiation workers shall not receive a dose in one calendar quarter greater than the following limits:

  • Whole body- 1.25 rem
  • Skin of whole body- 7.50 rem
  • Extremities- 18.75 rem

2. Individuals under 18 years of age are not permitted to receive a dose greater than 10% of the above limits.

3. The maximum permissible whole-body dose to a pregnant radiation worker during the pregnancy should not exceed 500 millirem.

4. Radiation levels to the whole body should not exceed 2 mrem/hr, or 100 mrem in 7 consecutive days, or 500 mrem/yr in unrestricted areas.

ALARA Commitment

Although occupational radiation doses from analytical x-ray equipment are very low and current occupational limits provide a very low risk of injury, Radford University recognizes that it is prudent to avoid unnecessary exposure. It is therefore the policy of Radford University to reduce occupational exposure to a level that is as low as reasonably achievable (ALARA). This will be accomplished through solid radiation protection planning and practice, as well as a commitment to policies that promote vigilance against unsafe practices.

Personnel Monitoring

All personnel who enter an area where it is likely they will receive greater than 10% of the maximum occupational dose limit shall wear a personnel monitoring device. The following rules will govern the use of personnel monitoring devices:

  1. The need for a personnel monitoring device will be determined by the RSO. The RSO will order, distribute, and collect the monitoring devices.
  2. Whole-body personnel monitoring devices shall be worn routinely on the waist, shirt pocket, or collar. Thermoluminescent dosimeters (TLD's) and film badges shall not be worn in the pocket or obstructed in any manner.
  3. When not in use, personnel monitoring devices shall be stored in an area where they will not be exposed to ionizing radiation above background levels.
  4. Badges are individually assigned and should be worn by one person.
  5. Personnel monitoring devices shall not be deliberately exposed to radiation except under the supervision of the RSO.
  6. Personnel monitoring devices are not to be worn during medical x-ray examinations. The badge is only for monitoring occupational exposure.
  7. Monitoring devices should be worn on the area of the body that is likely to receive the maximum dose.
  8. Pregnant radiation workers shall wear a whole-body monitoring device at the waist.
  9. All users of open-beam analytical x-ray equipment shall wear finger or wrist dosimetry devices.

Exposure Records

Exposure records will be maintained by the RSO. The RSO will notify workers at least annually of their exposure to radiation. The RSO will supply the user with a written report if a dose in excess of 25% of the occupational limits is received. The RSO will provide a radiation exposure report to the worker, or an employer, at the request of the worker.

Pregnant Radiation Workers

Pregnant radiation workers shall wear a whole-body monitoring device at waist level and be informed of their radiation exposure on a quarterly basis. A pregnant radiation worker should notify the RSO as soon as her pregnancy is known, limit exposure to less than 500 mrem, and strive to reduce her exposure to the very lowest practical level.

Inspections

To ensure that x-ray equipment is being used safely, all licensed activities are subject to inspection by the RSO. Inspections may be announced or unannounced and will be conducted at least every six months. A written report citing any deficiencies will be sent to the authorized user. The authorized user should correct the deficiencies within the time specified in the report unless a variance or an extension of time has been granted by the Radiation Safety Committee. An authorized user who disagrees with the deficiencies cited in the report may appeal in writing to the Radiation Safety Committee and request a hearing.

New Experiments

New experiments, which differ in size, kind, and/or scope from previous experiments, shall be submitted to the Radiation Safety Committee in writing and approved before the experiment can be performed. The documentation for new experiments shall include the following information and be initially approved by the RSO:

  • The purpose of the experiment.
  • A description of the experiment.
  • An analysis of the possible radiation hazards produced by the experiment.
  • Safety devices and procedures that will reduce hazards.

Equipment Requirements

Definitions

Analytical X-Ray Equipment - equipment used for x-ray diffraction and x-ray induced fluorescence analysis that examines the microscopic structure and\or composition of materials

Diffracted Beam - a beam composed of coherent mutually reinforcing scattered x-rays

Enclosed Beam Configuration - an analytical x-ray system in which all x-ray patterns are fully enclosed

Fail-Safe Design - a design feature that causes the beam port shutters to close or prevents emergence of the primary beam in the event a safety or warning device fails

Leakage Radiation - all radiation, except the primary beam, that comes from within the x-ray tube housing

Local Components - includes areas that are struck by x-rays such as radiation source housing, port and shutter assemblies, collimators, sample holders, cameras, goniometers, detectors, and shielding; but not including power supplies transformers, amplifiers, readout devices and control panel

Open Beam Configuration - an analytical x-ray system in which some part of the body could be placed in the primary or diffracted beam path

Primary Beam - x-rays which pass through an aperture in the source housing by a direct path from the x-ray tube

Safety Device - a device which prevents entry of any portion of the body into the primary beam path or causes the beam to shut off upon entry into its path

Scattered Radiation - radiation that has been deflected in its direction during interaction with an object

X-Ray Diffraction Equipment - an analytical x-ray device in which an x-ray beam strikes a sample, causing a portion of the beam to be diffracted

X-Ray Fluorescence Equipment - an analytical x-ray device in which an x-ray beam strikes a sample, producing x-ray fluorescence which is characteristic of the specimen

X-Ray Source Housing - portion of an analytical x-ray system that contains the x-ray tube

General Requirements For Open and Enclosed Beam Systems

Warning Lights - An easily visible warning light labeled, "X-RAY ON" shall be located near any switch that energize an x-ray tube and shall be illuminated only when the tube is energized. This light shall be of fail-safe design.

Labeling - All analytical x-ray equipment shall be labeled with a conspicuous sign that bears the radiation symbol and the words:

"CAUTION - HIGH INTENSITY X-RAY BEAM" on the x-ray source housing

"CAUTION RADIATION - THIS EQUIPMENT PRODUCES RADIATION WHEN ENERGIZED" near any switch that energizes an x-ray tube

Beam Trap - A beam trap or other primary beam shield shall be provided to intercept the primary beam after it has struck the sample.

Ports - Unused ports on the x-ray source housing shall be secured in the closed position to prevent accidental opening.

Additional Requirements For Enclosed Beam Systems

Chamber - The x-ray tube housing, sample detector, and analyzing crystal shall be enclosed in a chamber or coupled chambers that prevent entry of any part of the body.

Sample Chamber Closure - The sample chamber closure shall be interlocked with the power supply or shutter so that x-rays cannot enter the chamber while it is open. The interlock should be of fail-safe design.

Additional Requirements For Open Beam Systems

Safety Device - A safety device which prevents entry of any part of the body into the primary beam, or which causes the beam to shut off, shall be provided on all open beam systems. The safety device should be interlocked with the power supply or shutter and be of fail-safe design. An authorized user may seek an exemption from the requirement of a safety device by applying to the Radiation Safety Committee for a variance. Such application shall include:

  • A description of the safety devices evaluated and why they cannot be used.
  • A description of the alternative method that will be used to minimize the possibility of an accidental overexposure.
  • Procedures that will be used to alert personnel to the absence of a safety device.

Warning Devices - Open beam systems shall be provided with the following warning devices:

  • X-ray tube status (On-Off) located near the x-ray source housing, if the primary beam is controlled in this manner
  • Shutter status (Open-Closed) located near each port on the x-ray source housing, if the primary beam is controlled in this manner.

These devices shall be readily visible and properly labeled as to their purpose. Warning devices shall be of fail-safe design.

Shutters - Each port on the x-ray source housing shall be equipped with a shutter that cannot be opened unless a collimator or a coupling device has been connected to the port.

Operating Procedures

Procedure Manual - Normal operating procedures shall be written and available to all analytical x-ray equipment users. Analytical x-ray equipment shall not be operated differently from the manner specified in the procedure manual unless written permission has been obtained from the RSO.

Bypassing Safety Device - A safety device shall not be bypassed unless written permission has been obtained from the RSO. Approval shall be for a specified period of time. When a safety device has been bypassed, a conspicuous sign shall be placed near the x-ray tube housing bearing the words, "SAFETY DEVICE NOT WORKING".

Surveys

Radiation surveys of analytical x-ray systems shall be performed and documented:

  1. Upon installation of the equipment and at least once every six months thereafter to monitor leakage radiation
  2. Following any change in the initial arrangement, number, or type of local components
  3. Following any maintenance which requires the disassembly or removal of a local component
  4. During the performance of maintenance and alignment procedures which requires the presence of a primary beam and the disassembly or removal of a local component
  5. When a visual inspection of the local components reveals an abnormality
  6. Whenever personnel monitoring devices show a significant increase over the previous monitoring period

Posting

Each area or room in which analytical x-ray equipment is located shall be conspicuously posted with:

  1. A sign bearing the radiation symbol and the words, "CAUTION, X-RAY EQUIPMENT"
  2. State form " NOTICE TO EMPLOYEES - STANDARDS FOR PROTECTION AGAINST RADIATION"
  3. A notice which describes where the University Radiation Safety Manual, registration certificate, surveys, and inspections may be examined
  4. Procedures to be followed in the event of a radiological emergency

Radiation Limits

Enclosed Beam Systems - The exposure rate during normal operations shall not exceed 2.5 mrem/hr at a distance of 5 cm from the protective chamber walls.

Open Beam Systems - The exposure rate at the maximum rated current and voltage with all shutters closed shall not exceed 2.5 mrem/hr at a distance of 5 cm from the x-ray tube housing.

Generator Cabinet - The exposure rate at a distance of 5 cm from the surface of the x-ray generator cabinet shall not exceed 0.25 mrem/hr.

Scattered Radiation - During normal operations in restricted areas, scattered radiation in accessible areas shall not exceed 37.5 mrem/hr to the hands or 2.5 mrem/hr to the whole body from open beam systems

Alignment Procedures - The dose equivalent to the hands in any one hour shall not exceed 37.5 mrem.

Unrestricted Areas - The local components of an analytical x-ray system shall include sufficient shielding and be located and arranged so that exposure rates in unrestricted areas do not exceed 2 mrem/hr, or 100 mrem in seven consecutive days, or 500 mrem/yr to the whole body.

2.0  Properties of X-Rays

Introduction

X-rays were discovered in 1895 when Conrad Roentgen observed that a screen coated with a barium salt fluoresced when placed near a cathode ray tube. Roentgen concluded that a form of penetrating radiation was being emitted by the cathode ray tube and called the unknown rays, x-rays.

Like radio waves, light, and gamma rays, x-rays are a form of electromagnetic radiation. All electromagnetic radiation is characterized by the movement of massless waves of energy called photons. Photons travel at the speed of light and move with a characteristic wavelength and frequency that defines the specific type of electromagnetic radiation. The amount of energy carried by a photon is directly proportional to the frequency of the radiation and inversely proportional to the wavelength. Thus, x-rays which have a relatively short wavelength and high frequency possess a great deal of energy. X-rays are termed ionizing radiation because they contain sufficient energy to remove orbital electrons from atoms, creating ions.

X-rays have several interesting properties. Because of their short wavelength x-rays can penetrate materials that absorb or reflect visible light. Like light, x-rays can produce a visible image on photographic film. X-rays can produce biological changes in tissue that can be beneficial when used in radiation therapy. However, x-rays can also be harmful to biological organisms because of their ability to damage chromosomes. X-rays can also cause certain substances to fluoresce or emit radiations of longer wavelengths.

Because of these properties the use of x-rays has found wide applications in the fields of medicine, industry, and research. Physicians were using x-rays as a diagnostic tool within months of Roentgen's discovery. Industrial applications include the location of internal defects in materials, such as weld joints, and inspection of the internal parts of machinery. Principal applications of x-rays in research are x-ray diffraction and x-ray fluorescence analysis. These procedures are used to analyze both the chemical composition and crystalline structure of substances.

Production of X-Rays

X-ray Spectrum

X-rays are produced by two different mechanisms when high speed electrons collide with a metal target in a high vacuum. The resultant x-rays consist of a continuous spectrum known as Bremsstrahlung (German for braking radiation), and radiation with specific energies characteristic of the target material. Bremsstrahlung occurs when a high speed electron is deflected from its original course by the nucleus, losing part of its original energy as it slows down. This loss of energy results in an x-ray photon being produced in order to maintain conservation of energy. The energy of the x-ray photon is dependent on the angle of deflection of the incident electron and the amount of kinetic energy converted to x-rays. Thus, a continuous distribution of energies can be produced. Bremsstrahlung represents the predominant method of x-ray production in a medical diagnostic x-ray tube.

The second method x-rays are produced is termed the characteristic radiation effect. This results in the production of very specific radiations characteristic of the target material. Characteristic radiation is produced when an incident high speed electron collides with an orbital electron of the target material. The orbital electron is ejected from the atom creating a vacancy in the electron shell. An electron from a higher energy level falls into this vacancy releasing the excess energy in the form of an x-ray photon. Characteristic radiation is important in research because each element produces a characteristic spectrum that can be used to identify unknown samples. This forms the basis of x-ray florescence analysis. Characteristic radiation also constitutes the source of the high intensity monochromatic x-rays that is used in x-ray diffraction.

The X-ray Tube

An x-ray generating system requires a source of electrons, a means to accelerate the electrons, and a target to stop the high speed electrons. In 1913, Coolidge developed the basic type of x-ray tube that is still in use today. A typical tube, called a hot cathode x-ray tube, consists of a cathode with a tungsten filament for generating electrons, and a tungsten target embedded in a copper anode that stops the electrons. The filament is located in a concave cup that focuses the electron beam onto a small area of the target called the focal spot. Targets made of materials other than tungsten (e.g., copper) are usually used in diffractometers to generate low energy monochromatic x-rays. X-rays are directed out of the tube through a small window in the housing called a port.

Electrons are produced at the cathode by heating the tungsten filament to incandescence. The number of electrons is controlled by adjusting the temperature of the filament. The amount of charge flowing per second to the cathode is termed the current, expressed in milliamperage (mA). Electrons are accelerated towards the positive anode by a high voltage potential. This potential difference is expressed in kilovoltage (kV). Since the voltage across the tube may fluctuate it is usually expressed as peak kilovoltage (kVp). An electron drawn across a voltage of one volt has an energy of one electron volt (eV). The peak kilovoltage therefore defines the upper limit of the most energetic photon. From a practical standpoint, however, the energy of the average photon in the beam is approximately one-third the peak kilovoltage. Adjusting the kVp to 60 for example, will produce an x-ray beam having a maximum energy of 60 keV with an average energy of approximately 20 keV. Superimposed on this continuous spectrum will be the characteristic radiation of the target material.

Only a small percentage of the energy carried by the electrons are converted to x-rays upon striking the anode. Typically greater than 99 percent of the energy will be converted to heat and absorbed by the target. The target is usually cooled with water or oil to prevent it from melting.

Interaction with Matter

In passing through matter, energy is transferred from the incident x-ray photon to electrons and nuclei in the target material. An electron can be ejected from the atom with the subsequent creation of an ion. The amount of energy lost to the electron is dependent on the energy of the incident photon and the type of material through which it travels. There are three basic methods in which x-rays interact with matter: photoelectric effect, Compton scattering, and pair production.

Photoelectric Effect

In the photoelectric effect, an incident x-ray photon strikes an orbital electron and is totally absorbed by the electron. The electron is then ejected from the atom creating a vacancy in the shell. The ejected electron interacts with other atoms creating ionizations until it loses its kinetic energy. Electrons in the atom drop from the outer shells to fill the vacancy in the inner shell forming characteristic photons. Photoelectric absorption occurs predominantly in x-ray photons with energies below 10 keV.

Compton Scattering

Compton scattering occurs when an x-ray photon scatters from an orbital or free electron. Unlike the photoelectric process, only part of the photon's energy is transferred to the electron. The electron is ejected from the atom and the incident x-ray photon is scattered with a reduction in energy. This scattered photon continues to interact with orbital electrons by additional Compton or photoelectric processes. The probability of Compton scattering increases as the energy of the x-ray photon increase. At approximately 35 keV the probability of interactions through photoelectric and Compton collisions are about equal.

Pair Production

The third mechanism, pair production, is not encountered in analytical systems because the incident photon must possess a minimum energy of 1.02 MeV. In pair production, a photon interacts with the electric field around the nucleus and undergoes transformation into matter, with the creation of an electron and positron (positive electron). The positron is annihilated in microseconds by interacting with an electron, creating two 0.511 MeV gamma photons (annihilation radiation). These photons then interact with matter by Compton and photoelectric collisions.

3.0  Analytical X-Ray Equipment

X-Ray Diffraction

When a beam of monochromatic x-rays strikes matter, x-rays are scattered in all directions. In crystalline materials atoms are organized in an orderly manner with sets of parallel planes arranged in a lattice structure. Irradiating a crystal with monochromatic x-rays will result in x-rays emanating from the sample in an orderly pattern that is dependent on the position and intensity of each reflected beam. This directional dependence of the diffracted beam is called a diffraction pattern. It can be used to identify compounds, study phase transformations, determine crystalline size, measure stress or strain, and other similar structure related properties of materials. Since x-ray diffraction is applicable to the study of most solid materials, it has found wide use in a variety of fields including chemistry, physics, mineralogy, ceramics, metallurgy, biology, and medicine.

In a typical diffractometer, the primary beam passes from the tube through a shutter in the x-ray tube housing. A filter is often inserted close to the shutter to filter out the continuous x-ray spectrum while allowing a high percentage of the characteristic x-rays through. The energy of the characteristic radiation is dependent on the target material and beam energy.

The beam passes through a collimator which limits the cross section of the beam to approximately 1 sq mm and strikes the sample creating a characteristic diffraction pattern. The diffracted x-rays are recorded on film or by a Geiger, proportional, or scintillation counter for further study. The detection device travels through a circular path on a device known as a goniometer. Only a small fraction of the primary beam impinges on the sample. The beam then strikes a beam trap which absorbs the remaining x-rays.

The x-ray diffractometer is designed for continuous operation in contrast to diagnostic x-ray tubes which typically stay on for a fraction to a few seconds. Consequently, all connections in the diffractometer must be tight to prevent leakage and scattered radiation.

X-Ray Fluorescence Spectrometers

Fluorescence x-ray spectroscopy is an analytical method for determining the elemental composition of a substance. The sample is irradiated with high intensity x-rays generated from a tungsten target. Characteristic x-rays are emitted and the spectrum is analyzed in an x-ray spectrometer. The elements present in the sample can be identified by their characteristic wavelengths. The relative proportion of the elements can be estimated by the respective intensities of the lines.

High intensity beams of fairly penetrating radiation are utilized in this method. The instruments are usually completely enclosed to minimize scattered radiation and to prevent access to the primary beam. To prevent accidental exposure to the x-ray beam, sample chamber doors are provided with safety interlocks. The sample is usually placed very close to the x-ray port. Serious burns have been received as a result of insertion of the finger into the sample chamber while the unit was operating.

Nature of the Radiation

Typical acceleration voltages are 25-50 kilovolts for diffraction tubes and 25-100 kilovolts for fluorescence tubes. Tube currents are approximately 20 milliamps. The maximum energies of the x-rays produced are therefore 50 keV for diffraction tubes and 100 keV for fluorescence tubes. The Bremsstrahlung effect produces a continuous energy spectrum extending from approximately 5 keV to 100 keV. The maximum intensity is in the range of 20 to 30 keV. Although energies below 5 keV are produced, these x-rays are readily attenuated.

Superimposed on the continuous spectrum are the characteristic lines of the target material in the anode. These constitute less than half of the x-ray intensities in the case of diffraction tubes. Characteristic x-ray energies from various target materials include Cr (5.4 keV), Fe (6.4), Co (6.9), Cu (8.0), and Mo (17.5). These radiations are usually called "soft" x-rays because they are readily absorbed in matter. Fluorescence tubes typically use tungsten targets which have characteristic lines around 60 keV.

Analytical x-ray equipment produces beams that are very narrow (1 mm2) and highly intense. Exposure rates at the x-ray tube port where the primary beam exits the housing may be as high as 400,000 R/min. As the beam exits the collimator exposure rates may still be several thousand R/min. Diffracted beams from the sample may be several R/min. and scattered radiation from objects in the beam path can deliver exposure rates of several hundred mR/hr.

Fortunately, because of the low energy of these radiations, only relatively thin layers of shielding are required to attenuate the x-rays. It is this property, however, that make these x-rays so dangerous to the skin. Low energy x-rays are highly absorbed in soft tissue and severe and permanent local injury can result from exposure to the primary or diffracted beams.

Radiaton Hazards

Hazardous radiation from x-ray diffraction and fluorescence equipment may result from exposure to the primary beam, scattered radiation, diffracted beam or the high voltage power supply unit.

The primary, uncollimated beam close to the tube housing is the most hazardous because of the extremely high dose rates. Accidental exposure of only a few seconds can cause severe burns to the fingers, hands, eyes, or arms. Accidents of this type can occur from insertion of the fingers into sample chambers and by dismantling shutters when the x-ray beam is on.

Primary beam radiation can also leak through small cracks around loose fittings or through pin-hole openings in the shielding or tube housing. The primary beam can also penetrate through shutters that do not close properly. Exposure to the primary beam may also occur as it exits from the collimator. Although the primary beam contains highly intense radiation, its small cross section reduces the risk of high doses being received by the whole body.

Scattered radiation near the x-ray housing, ports, and shutters produced from the primary beam can be very intense and cause serious injury. Primary beam radiation striking the sample, shielding, and equipment can also scatter into the room and expose personnel to chronic low level radiation.

Diffracted beams from the sample have high exposure rates and small cross sections. These beams can be directed from the sample at almost any angle and expose workers to unnecessary radiation. Although dose rates are seldom high enough to produce serious injury from diffracted beams, it is desirable to provide shielding against this radiation.

Another potential source of radiation exposure to personnel working with analytical x-ray equipment comes from exposure to the high voltage power supply units. Rectifier tubes in these units may become gassy and emit very penetrating radiation.

Safety Devices

Shielding

Shielding must be adequate to ensure that stray radiation escaping into the room does not exceed permissible dose limits and is as low as reasonably achievable. Because x-ray energies are relatively low, it is usually easy to provide adequate shielding. Background levels around analytical x-ray equipment can usually be kept well below legal limits with a minimum of effort. Even materials such as Plexiglass can provide a considerable amount of protection.

The most important concern is to protect workers from exposure to the primary beam which can cause serious injury within a few seconds. The main protection from exposure to the primary beam is the x-ray tube housing. An x-ray tube should never be turned on unless the housing is in place. The thickness of the shielding as supplied by the manufacturer is usually sufficient to ensure protection from excessive radiation doses. Leaks, however, can occur at higher voltage if the shield is defective or too thin.

Lead shielding is typically used for absorption of the primary beam. For example, 2 mm of lead will reduce the dose rate by a factor of 1011 for x-rays generated at 50 kVp. Shielding around the port and shutter assembly should be designed with labyrinth-type joints to avoid any straight paths. Care should also be taken to avoid cracks or small openings in the shielding material. All joints and shielding should be checked with a survey meter to ensure that they are leak tight.

Although dose rates from scattered radiation and the diffracted beam are usually not high enough to cause serious local injury, appropriate shielding should be provided. These radiations are usually very weak and dissipate rapidly because of their low energy, divergence, and high absorption in air. The equipment itself provides some shielding but additional shielding in the form of 6 mm thick Plexiglass may be needed. When flexible shielding is needed "lead" aprons with a lead equivalency of 0.25 mm can be used as an effective barrier against scattered radiation. Aprons should be inspected periodically to ensure that radiation does not leak through cracks in the material.

Ports

In diffraction equipment the housing may contain up to four ports to allow the primary beam to exit from the tube. Unused ports must be effectively closed to prevent the beam from emerging and accidentally exposing a worker. Ports must be secured in such a manner that tools are required to open the ports. Wing nuts, tape, etc., should not be used to secure the port. Shielding around the port must be properly constructed of leak-proof joints to ensure that high intensity scattered radiation does not escape from the tube. For example, equipment should not be simply butted up against the tube port. There must be considerable overlap in the shielding and right angles introduced into the beam path to prevent radiation from escaping through small gaps.

Shutters

The shutter is located immediately in front of the port of the tube and behind the collimator coupling. The purpose of the shutter is to place a piece of highly absorbant material such as lead in front of the port to block the emergence of the primary beam. The shutter gate is contained inside a leak-proof compartment with appropriate labyrinth joints to prevent the escape of radiation.

Ports that are in use must be properly fitted with a safety shutter that cannot be opened unless a collimator or a coupling has been connected to the port. Removal of a collimator must cause the shutter to automatically close. The shutter should be connected to a warning light or other device to warn the operator that the shutter is open.

Safety shutters may be purely mechanical devices or electrically operated. Mechanical shutters are usually more reliable but electrically operated shutters offer greater versatility. Gravity and spring-loaded shutters must close quickly and completely and not permit attached equipment to be withdrawn a considerable distance before closing. Care should be taken with spring-loaded shutters because the spring can weaken or break. Spring assisted shutters should fall from gravity if the spring breaks. Electrically operated shutters are inexpensive and often used to update old equipment. Microswitches operating in parallel are connected to the shutter gate and the attached equipment. The equipment must be properly in place to depress the pin before the shutter will open.

Collimator

Collimators are connected to the shutter to limit the size of the x-ray beam and reduce the amount of background scatter. By reducing the size of the beam, serious injury to the whole body is reduced. Decreasing background radiation reduces the radiation dose to personnel and produces a cleaner signal in the detection device. The collimator must be electrically or mechanically interlocked with the shutter.

Care must be taken to ensure that the coupling between the tube and the collimator is tight. Intense beams of scattered radiation can be produced when the primary beam strikes the collimator. Shielding material must be of adequate thickness, connections must overlap, and straight paths from the tube to the outside should be avoided.

Sample Chamber

All fluorescence units and some x-ray diffraction equipment may include a chamber that contains the sample under investigation. To prevent serious burns, sample chamber covers must be interlocked to the main power supply or shutter to prevent the insertion of fingers into the chamber while x-rays are being produced. Microswitches are commonly used to interlock the cover, although mechanical interlocks are sometimes used.

Interlocks

Interlocks are used to prevent access to the primary beam by either cutting off the high voltage supply or closing the shutter. Interlocks are commonly found on the shutter-collimator assembly, sample chamber cover, and/or the safety enclosure. Electrical interlocks in the form of microswitches are most commonly used. Plug and socket-type connections can also be used as an effective interlocking device. If possible, interlocks should be installed in the fail-safe mode (i.e., if they fail the equipment will not operate or the shutter will not open).

Interlocks must be reasonably reliable and not subject to accidental over-riding. Deliberately overriding an interlock is forbidden except for alignment purposes or if permission has been granted by the Radiation Safety Officer. Signs should be conspicuously posted if the interlock has been defeated.

Interlocks are strictly a safety device and should not be used to turn equipment off or close shutters. It should be necessary to return to the control panel to re-start the equipment once an interlock has shut the equipment down. It should not be possible to simply re-start the equipment by depressing the pin of the microswitch.

Beam Trap

Only a small portion of the primary beam is absorbed or diffracted by the sample. The x-rays that pass through the sample are absorbed by a beam trap. This device reduces scattered radiation and possible exposure to the primary beam. The beam trap consists of a hollow cylinder with a bottom covered by a highly absorbant material. Approximately 2 mm of lead is typically used. In order to reduce scattered radiation, care must be taken to ensure that the beam does not strike the walls of the cylinder. Ideally, the beam trap should be interlocked with the shutter or main power supply in case the trap is moved out of its normal position. It is also a good idea to place a second permanent beam stop beyond the movable beam trap.

Safety Barrier

Whenever possible, a safety barrier should be installed to prevent the operator's hands from accidentally being placed in the x-ray beam. This device should be interlocked to the shutter or main power supply. The safety barrier also functions to reduce scattered radiation in the room.

Because of the low energy of the x-rays, safety barriers are typically made from Plexiglass. Holes can be cut into the plastic so that tools can be inserted without risk of exposure. If it is not practical to erect a plastic cage around the equipment, wire mesh can be used as a physical barrier. Barriers can also be made from a light beam connected to a photo-cell that shuts off the x-ray beam when the beam of light is interrupted by a hand.

In some situations, it may be impossible to provide a safety barrier. Examples include the study of large bulky items, frequent attachment and configuration changes, need for making adjustments with the x-ray beam on, and the specimen and detector move over wide angular limits.

Open beam equipment without a safety barrier should be used in a separate room. Access to the room should be restricted while the equipment is running. A warning light connected to the main power supply of the equipment should be placed at the door. Signs should be posted to warn personnel of open beam systems. This type of equipment should only be used by highly trained and experienced personnel. Undergraduate students should be restricted to working with systems equipped with safety barriers.

Warning Devices

Warning lights interlocked to the main power supply or the shutter should be provided at the on-off switch and near the tube housing to remind the operator that the x-ray beam is on. In addition, a light or other device should be provided to warn the operator when the shutter is open. Warning lights should be of fail-safe design so that the generator will turn off or the shutter closes if the light fails.

4.0  Radiation Protection Measures

Time

The dose of radiation a worker receives is directly proportional to the amount of time spent in a radiation field. Thus, reducing the time by one-half will reduce the radiation dose received by one-half. Operators should always work quickly and spend as little time as possible around the equipment while it is operating. In addition, the x-ray tube on-time should be as short as possible to accomplish the desired results.

Distance

Radiation exposure decreases rapidly as the distance between the worker and the x-ray source increases. The decrease in exposure from a point source, such as an x-ray tube, can be calculated by using the inverse square law. This law states that the amount of radiation at a given distance from a point source varies inversely with the square of the distance. For example, doubling the distance from an x-ray tube will reduce the dose to one-fourth of its original value, and increasing the distance by a factor of three will reduce the dose to one-ninth of its original value. Although the inverse square law does not accurately describe scattered radiation, distance will still dramatically reduce the intensity from this source of radiation. Maintaining a safe distance, therefore, represents one the simplest and most effective methods for reducing radiation exposure to workers. Using the principle of distance is especially important when working around open beam analytical x-ray equipment.

Shielding

Radiation exposure to personnel can also be reduced by placing an attenuating material between a worker and the x-ray tube. The energy of the incident x-ray photon is reduced by Compton and photoelectric interactions in the shielding material. Thus, substances such as lead, that are very dense and have a high atomic number, are very practical shielding materials because of the abundance of atoms and electrons that can interact with the x-ray photon. Shielding is often incorporated into the equipment, such as the metal lining surrounding the x-ray tube. It may also consist of permanent barriers such as concrete and lead walls, leaded glass, and plastic movable screens in the case of analytical x-ray equipment. Shielding can also be worn by personnel. Examples include lead impregnated gloves and aprons, eyewear, and thyroid shields.

The amount of shielding necessary to reduce the radiation intensity to a desired level can be calculated from the half-value layer of the material. The half-value layer is the thickness of the material necessary to reduce the radiation intensity to one-half of its original intensity. When calculating shielding needs, it is helpful to remember that seven half-value layers will reduce the radiation level approximately 100 times, and ten half-value layers will reduce the radiation level by a factor of 1000.

Radiation Protection Guides

Traditional Units

The units associated with radiation measurements must be understood in order to properly interpret radiation monitoring equipment and protection guidelines. The units traditionally used to measure radiation are the roentgen, rad, and rem.

The roentgen (R) is a unit for expressing exposure from x or gamma radiation in terms of the number of ionizations produced in air. One roentgen of radiation will produce ionizations equal to one electrostatic unit of charge in one cubic centimeter of dry air at standard temperature and pressure.

The roentgen defines a radiation field in air but does not provide a measure of absorbed dose in ordinary matter or tissue. When radiation passes through an object, part of the energy will be transferred to the material. This is referred to as the absorbed dose. In order that absorption properties of the exposed material be taken into account, a dose unit has been developed called the rad (radiation absorbed dose). In contrast to the roentgen, the rad is used to express the radiation dose absorbed in any medium from any type of radiation. One rad is equal to the amount of radiation that results in the absorption of 100 ergs per gram in any material. It is approximately equal to the absorbed dose delivered to soft tissue by one roentgen of x or gamma radiation.

In terms of human exposure, however, another factor must be considered; exposure to equal doses from different types of radiation do not result in equal damage to biological tissue. Therefore, in order to account for these varying effects, a unit is employed termed the rem (roentgen equivalent man). The rem estimates the amount of any radiation that would be necessary to produce the same biological effects in humans as one rad of x or gamma radiation. The rem is equal to the rad multiplied by a quality factor that estimates the relative biological effectiveness of different types of radiation. This biological effectiveness depends upon the number of ionizations created per unit distance in tissue as the radiation travels through the body. The quality factor for x-rays is one, however, quality factors for other types of radiation can be as high as twenty (e.g., alpha, particles). Therefore, a dose of 0.05 rads from alpha particles could do the same biological damage as 1 rad of x-rays because both equal one rem (0.05 rads x 20 quality factor). One advantage of using rem units is that dosages delivered from different types of radiation become additive.

In summary, the roentgen is a unit of exposure, the rad is a unit of absorbed dose, and the rem is a unit of biological dose. The rem is the unit that is used to measure radiation doses to personnel. For practical purposes, however, the roentgen, rad, and rem are essentially equivalent for x-rays and can be used interchangeably. Commonly used subunits are milliroentgen, millirad, and millirem (mR), which are equal to 1/1000 of these units.

International System (SI)

Recently new radiation protection units consistent with the metric system or International System of Units (SI system) have been adopted. There is no unit comparable to the roentgen in the SI system. This was done to phase out the use of this quantity. The new SI unit for absorbed dose, which replaces the rad, is the gray (Gy). One gray is equal to 100 rads. The new unit for the rem is the Sievert (Sv), which is equivalent to 100 rem. Although SI units are accepted internationally, the roentgen, rad, and rem continue to be widely used in this country.

Maximum Permissible Dose (MPD)

To protect radiation workers and the public, maximum permissible dose limits have been established by the National Council on Radiation Protection (NCRP). The MPD is the dose of radiation, based on current knowledge, that a person can receive without sustaining appreciable bodily injury. The maximum whole-body dose allowed to radiation workers is 5 rem per year or 1.25 rem per quarter. Dose limits to the skin are 30 rem per year or 7.5 rem per quarter. The MPD for the extremities is 75 rem per year or 18.75 rem per quarter; reflecting the decreased sensitivity to radiation damage of these areas. Radiation workers under the age of 18 are limited to 10% of these values. The limit for the public has been set at 2 mR/hr, or 100 mR for seven consecutive days, or 500 mR/yr. Doses to the public, however, should average less than 100 mR/yr over several years. The dose limit for pregnant radiation workers was set at 500 mR during the course of the pregnancy.

Because any amount of radiation is potentially harmful, the NCRP has officially adopted the ALARA concept. This principal states that all radiation exposures should be kept "as low as reasonably achievable". Maximum permissible doses have been established as reasonable risks comparable to other industries. These doses should be thought of as absolute ceiling levels and not as "safe" limits. Radiation workers should always strive to reduce doses to ALARA levels by using proper safety procedures and techniques.

5.0  Radiation Monitoring

Survey Instruments

Radiation survey instruments are used to detect potential radiation hazards, measure radiation intensities, monitor the effectiveness of shielding arrangements, and estimate exposure to personnel. There are two main categories of radiation monitoring devices: gas filled detectors and scintillation detectors.

Gas detection instruments are based on the principle that ions are produced when radiation passes through a gas-filled chamber. Electrons liberated in the chamber are attracted to the center electrode (anode) by a positive voltage potential. Positive ions are attracted towards the walls (cathode) of the chamber. This produces an electrical pulse or current which can be detected and recorded on an instrument known as a scaler.

There are three types of gas filled radiation detectors: ionization chambers, proportional counters, and geiger-mueller detectors. The primary difference between these detectors is the voltage applied to the chamber. The kind of detector used is based on the intensity and the type of radiation field encountered. Scintillation detectors operate on the principle that certain materials scintillate or give off light when exposed to radiation. There are two major types of scintillation detectors, crystal and liquid.

Ionization Chambers

At very low applied voltages, ion pairs created by radiation passing through the chamber may recombine before they are collected and counted. As the voltage of a gas filled detector is increased, virtually every ion pair produced by the incident radiation will be captured. The current flowing through the meter is therefore directly proportional to the activity of the source. This feature makes these detectors very useful as radiation monitoring devices. Survey instruments operating at this voltage are called ionization chambers or "cutie pies". Because almost all ion pairs are collected, this instrument is used when it is necessary to accurately determine exposures. Ionization chambers are also used to determine exposures in areas of high radiation intensities. Ionization chambers, however, lack sensitivity and are relatively slow to respond to changing fields and are not useful for detecting leaks in analytical x-ray systems.

Proportional Counters

As the voltage of the tube is increased further, electrons experience greater acceleration and achieve sufficient energy to create secondary ionization and electrons in the gas. This amplification is termed an avalanche and dramatically increases the size of the electrical pulse at the central anode. Gas multiplication can create millions of ion pairs per ionizing event, in contrast to the ionization chamber which creates one ion pair. Although an avalanche has occurred, gas amplification is proportional to the energy of the initiating event in this voltage region. Radiation monitoring devices operating in this region are called proportional counters. With sufficiently thin windows alpha particles, which produce a large number of ions in the gas, can be distinguished from beta particles. In addition, the counter can be used to measure the energies of incoming x-rays and is often used as a detector in analytical x-ray equipment.

Geiger-Mueller (GM) Counters

Primary ionizations produced by the incident x-ray photons are accelerated by a very high voltage potential in a Geiger-Mueller Counter. Secondary ionizations are created from collisions with the accelerated ions. The secondary ions, in turn, are also accelerated and achieve sufficient energy to create ions. This process continues with the resulting formation of an avalanche of billions of ion pairs produced from a single ionization event. Because of this avalanche of electrons, a very large electrical pulse is produced a the anode making the GM counter a very sensitive device for the detection of radiation. A small amount of a halogen gas is often added to the tube as a quenching agent to stop the avalanche. The size of the electrical pulse is independent of the type of initiating radiation depositing energy in the tube. Unlike the proportional counter, GM counters cannot distinguish between types of radiation or energies. Because gas amplification has now reached its maximum volume, the same current flow will result regardless of the number of primary ions produced by a single incident photon.

The GM counter is the most widely used area survey instrument for the detection of low-level radioactive contamination and leaks in shielding arrangements. It is very sensitive, relatively inexpensive, and rugged. With sufficiently thin windows, alpha, beta and low energy x-rays can be detected. Besides being unable to distinguish between different ionizing events, GM counters will respond differently when exposed to the same dose rate produced by photons of different energies. Therefore, GM counters should only be used as a detection instrument and not for quantitative measurements of radiation unless they have been specifically calibrated for those energies.

Another major disadvantage of GM counters is their limitation to low radiation fields, typically below 200 mR/hr. Once ionizations have been initiated in a GM tube it becomes insensitive for a short time, called the dead time, and will not respond to further ionizing events. As a result, the number of counts recorded will be less than the true count rate. This error is relatively small at low radiation intensities, however, in high radiation fields large errors can be introduced. At very high exposure rates, where events are interacting with the tube much faster than the dead time, the counter may actually saturate and read zero.

Scintillation Detectors

Scintillation detectors release light when exposed to x-rays or gamma rays. Scintillation detectors are of two types: solid and liquid. Most solid scintillation crystals are composed of sodium iodide with a small amount of thallium added as an "activator". The crystal is coupled to a photomultiplier tube that converts the light flashes to amplified electrical pulses. The number of pulses are directly proportional to the intensity, and the size of the pulse is directly proportional to the energy of the incident radiation. These pulses are then analyzed by a counter, spectrometer, oscilloscope, or computer.

Because scintillation crystals are solid, rather than gaseous, their higher density and atomic number makes them very efficient and sensitive instruments for the measurement of x-rays and gamma rays. Portable scintillation detectors are even more sensitive than GM counters because of their increased efficiency. Scintillation detectors, however, are not as rugged as geiger counters because the crystal is hygroscopic and can absorb water from the atmosphere.

Liquid scintillation detectors employ organic compounds that give off light when radioactive materials are added to the solution. The light is detected by photomultiplier tubes and analyzed and counted in a manner similar to solid scintillation detectors. These types of detectors are commonly used to detect weak alpha, beta, and gamma radiations.

Surveying Analytical X-Ray Equipment

Instrumentation

Radiation surveys should be conducted with a thin window (1-2 mg/cm2) geiger counter and a low energy ionization chamber. With its fast response and sensitivity, the geiger counter is ideal for detecting leaks in the shielding and around couplings. Once the leak has been detected, the exposure rate can be accurately determined with a low energy ionization chamber. Care should be taken in the choice of instruments to ensure they are sensitive to the energy of the x-rays being generated, and have been calibrated for low energy x-rays.

The exposure rate from leakage and scatter may vary from a few mR/hr to several R/hr. Surveyors should be aware that geiger counters can saturate and read zero when placed in high radiation fields. Ideally, the geiger counter should be used with an audible indicator. This gives an immediate response to radiation and allows the surveyor to watch the placement of the probe.

Measurements of exposure rates with a detector that has a cross sectional area greater than the x-ray beam will result in readings less than the true value if the instrument was calibrated in a field with a large cross section. Correction factors of 6000 or more may be required for typical instruments. An approximate correction can be made by multiplying the measured value by the ratio of the detector area to the beam area. Accuracy, however, is not of prime importance when surveying analytical x-ray equipment. The geiger counter should be used to detect leaks and to trace the leaks back to their source. Appropriate actions, such as adding shielding, can then be taken to correct the problem.

Monitoring Techniques

Monitoring should be conducted periodically and whenever the arrangement or design of the equipment is changed. Analytical x-ray equipment should be surveyed to detect and correct unsafe conditions that could lead to excessive radiation exposures to workers and the public. The following procedures should be followed when surveying analytical x-ray equipment:

  1. Note the location and function of the various components including switches, warning lights, x-ray tube, shutters, ports, collimators, and the beam trap.
  2. Ensure that unused x-ray ports are effectively shielded and secured.
  3. Check the shutter for smooth operation.
  4. Equipment should have no missing parts; shielding and couplings should fit properly and be properly secured.
  5. Any modifications to safety device should be noted.
  6. Check for radiation damage or corrosion to parts exposed to the primary beam.
  7. Ensure that warning labels and signs are properly posted.
  8. Place a sample in position, turn the tube on to the normal maximum voltage and current.
  9. With all shutters closed, check the tube housing and shutter couplings for leakage. Open the shutter and check all areas around the shutter, collimator, sample, and ports for excessive scattered radiation levels. Do not place the probe into the primary or diffracted beam path. Check the equipment throughout its range of motion.
  10. Monitor the radiation levels at the boundary of the equipment to ensure that radiation levels to the public are within acceptable limits.
  11. Track small leaks back to the source and apply lead foil to the area that is leaking radiation.
  12. Diffraction units with more than one operational port should be checked individually.

Personnel Monitoring

Personnel monitoring is used to detect and measure radiation exposure to individuals. The purpose of personnel monitoring is to document the exposure a worker receives in order to determine if radiation exposure limits have been exceeded, and to aid in keeping exposures as low or reasonably achievable. Personnel monitors are relatively inexpensive, reasonably reliable, and portable. They are usually worn on the belt, shirt pocket, collar, or finger. Personnel monitoring devices designed to measure low energy radiation should not be worn in a shirt pocket.

Personnel monitoring is required if there is a possibility that a radiation worker will receive greater than one-fourth of the maximum permissible dose (MPD). However, monitoring devices are usually issued if there is a possibility that a worker will receive greater than 10% of the MPD.

Whole body badges are generally used to measure large radiation fields such as those that might be encountered from diagnostic x-ray units. These badges are of limited value when working around analytical x-ray equipment. Scattered radiation is of low energy and easily attenuated by the air. In addition, small diffracted beams may not be detected by the badge.

The use of finger badges can be of some value to detect scatter radiation and increases the probability of detecting exposure to the diffracted or primary beam. However, due to the small diameter of the beam, exposure to the fingers may go undetected.

Although finger and whole-body badges may be of limited value in describing the radiation dose to a worker, they can be helpful. Increased exposure, where no exposures were noted in the past, might point to leakage, an unsafe safety device, or unsafe operating procedures. Operators of open beam equipment and those who assemble and align systems, must wear finger badges and should wear whole-body badges. Operators of units that are completely closed, have no measurable scattered radiation, and cannot be operated with an open beam should wear finger badges.

Film Badges

The film badge consists of one or more photographic emulsions contained in light tight envelopes inside a plastic holder. These emulsions have varying degrees of sensitivities to x-rays, gamma rays, beta particles, and neutrons. Windows and filters are built into the badge to distinguish between different types of radiation. An estimation of radiation energies can also be made. The film is developed and the density of the exposed film is proportional to the exposure received by the film badge. The degree of darkening is then compared with film exposed to known quantities of radiations. Film can also discriminate between primary beam exposure and scattered radiation. Scatter radiation produces a fuzzy image while a distinct image is produced from primary beam exposure.

Film badges have several advantages that have made them the most popular form of personnel monitoring devices. They are inexpensive, reasonably accurate and sensitive, provide a permanent record of exposure, and supply information on the type and approximate energy of the radiation exposure.

Film badge monitors also possess several disadvantages that have led to a decline, recently, in their popularity. Film badges are not as accurate or reliable as other personnel monitoring devices, nor do they detect exposures from low energy photons very well. In addition, film badges are relatively insensitive, the lower limit of detection is typically between 20 to 30 mR. Artificially high readings can result from false darkening as a result of improper handling, heat, humidity and age. In order to limit false darkening, film badges should not be worn for periods in excess of a month.

Pocket Dosimeters

Pocket dosimeters are small, pencil shaped ionization chambers that directly measure ionizations due to radiation. The chamber is charged before use and a scale is adjusted to read zero at this voltage potential. As radiation passes through the chamber, ions are created. These ions are collected at the electrodes of the chamber and neutralize or discharge the dosimeter. This discharge is directly proportional to the quantity of radiation entering the chamber and is read on a voltage meter that is calibrated in radiation units. Some pocket dosimeters can be read directly from an internal scale while others must be inserted into a dosimeter reader.

The major advantage of a pocket dosimeter is its ability to supply an immediate readout of radiation exposure. Because of this, pocket dosimeters are typically used only in high radiation area. It is important to ensure that the dosimeters can detect the energy of the x-ray field being emitted. Pocket dosimeters are also reasonably accurate and sensitive, however, they are expensive, easily damaged, and give false readings due to charge leakage.

Thermoluminescent Dosimeters

The newest type of personnel monitoring device, which is rapidly becoming the most popular, is the thermoluminescent dosimeter (TLD). This device looks similar to a film badge but uses a calcium fluoride or lithium fluoride crystal to measure radiation exposure. When radiation strikes the crystal, electrons absorb the energy and are promoted to higher energy states in the crystalline lattice. Upon heating, these excited electrons fall back into their original energy states releasing the stored energy as ultra-violet light. The amount of this light is directly proportional to the radiation dose received by the crystal. The light is then quantified by a photomultiplier tube.

TLD monitors have several advantages and few disadvantages. They are more accurate, reliable, and sensitive than film badges and pocket dosimeters, and their response to low as well as high energy photons is more uniform. These properties make them ideal for use around analytical x-ray units. TLD monitors are also relatively sensitive; radiation doses as low as 5 mR can be detected. TLD monitors are not influenced by normal heat and moisture, which allows the monitors to be worn for as long as three months without loss of information. TLD monitors are also reusable, having lost the "memory" of the previous radiation exposure when heated. They can also be read quickly so that radiation doses can be obtained within a few minutes.

The primary disadvantage of TLD monitors is cost. The monitoring program can be twice as expensive as film badge monitoring. However, this cost can be reduced because TLD monitors can be read every three months instead of monthly. Costs are expected to be lowered in the future and TLD monitors will probably replace film badges as the method of choice in personnel dosimetry programs.

6.0  Biological Effects of Ionizing Radiation

Exposure of the human body to ionizing radiation can result in harmful biological effects. The nature and severity of the effects depends primarily on the dose of radiation absorbed and the rate at which it is received. Exposure to radiation can result in radiation burns and sickness, cancer, genetic defects, and abnormalities in unborn children. Very large doses of radiation to the whole body can result in death. These effects have been observed in people exposed to radiation in a variety of situations including therapeutic x-rays, radiation accidents, and the Japanese A-bomb survivors.

Radiation Burns

Radiation burns were first noted within a month of Roentgen's discovery of x-rays. Within a year, it was widely known that radiation workers had to take precautions to avoid injury. Today, great efforts are made to protect workers from accidental exposure but radiation induced injuries still occur. Severe local injury may result when a worker is exposed to a high dose of radiation for a short period of time. Symptoms may range from reddening of the skin, swelling and blistering, to tissue death and amputation of the affected area.

Accidental exposure to the primary beam from analytical x-ray equipment may result in high radiation doses to localized areas of the body. The hands, fingers, and eyes are the parts of the body most commonly at risk. The nature and severity of the symptoms depends on the dose, exposure time, energy, and susceptibility of the individual. The smallest dose to the skin that will result in visible damage is approximately 300 rem. Reddening of the skin, called erythema, may occur 2-3 weeks after the exposure in highly susceptible individuals. Typically, however, the dose must exceed 600 rem before radiation burns become apparent. These burns are equivalent to first-degree thermal burns similar to a mild sunburn. There are no initial symptoms from the over-exposure and the worker may be unaware of an injury.

Within a few hours, the person exposed may feel a sensation of warmth or itching followed by an initial reddening of the skin. The reddening may fade after a few more hours or days and reappear 2-3 weeks later. The skin is likely to start peeling at this time. Although not necessary, medical help may be sought to prevent further injury and infection. Recovery should be fairly complete with no complications.

Damage to the eye can result from an acute exposure to x-rays greater than 600 rem. The lens is the most radio-sensitive part of the eye. At this dose, the lens will become cloudy and form a cataract. Highly sensitive individuals may start to develop cataracts from exposure to as little as 20 rem. Depending on the energy of the incident radiation damage to the cornea may also occur. To prevent damage to the eyes, workers should always wear protective eyewear when working with open beam systems.

Exposure to an acute dose between 1000-2000 rem will produce serious tissue damage similar to a second degree heat burn. Reddening, inflammation, swelling, and tenderness will occur within a few hours after the exposure. Blisters will develop 1-3 weeks later. The blisters will break open leaving raw, painful wounds that are vulnerable to infection. Hands will become stiff and finger motion is painful. Medical attention is required to relieve pain and prevent infections. Visible damage may heal within a few months. However, permanent damage to tissues and blood vessels may occur.

An acute exposure of between 2000-3000 rem to a small area of the body will cause an injury similar to scalding or chemical burn. Intense pain and swelling will occur within hours of the overexposure. Medical treatment is urgently needed to reduce pain. Surgical removal of the exposed tissue and skin grafting may be required to promote healing. Blood vessels will also be destroyed by the intense radiation. Amputation of the affected area may be necessary. Pain, repeated injuries to the area, and reopening of the wound can be expected to occur in the future. Animal studies suggest that the risk of developing malignant skin cancers is at its highest from exposure to x-rays in the 2000-3000 rem range. Exposure to tissue from radiation doses above 3000 rem will completely kill the tissue and underlying blood vessels and require surgical removal.

Localized exposures between 5000 and 10,000 rem gradually received over a period of months to years will result in an eczema-like condition to the skin. Chronic irritation, inflammation, dryness, and itching that seldom heals completely, can result. Open sores may erupt periodically and the recuperative powers of the skin are markedly reduced. Malignant skin cancers may also occur in a large proportion of these cases.
 
Radiation Sickness

Radiation burns occur when a large dose of radiation is received by a small part of the body. Severe damage and tissue death may occur but the exposed person usually survives. If a large dose of radiation, however, is delivered to the whole body of an individual in a short period of time, severe illness or death may occur. The sequence of events that follows exposure to high levels of radiation to the whole body is termed radiation sickness or the "acute radiation syndrome".

Radiation doses to the whole body greater than 100 rem delivered within a few hours, are usually necessary to produce noticeable symptoms. Changes in the blood, however, can be observed from exposures as low as 25 rem.

Symptoms usually become apparent within a few hours or days depending on the dose received. The first stage of radiation sickness is often characterized by nausea, vomiting, and diarrhea. Following this initial period of sickness, symptoms may subside and the individual may feel well. This stage can last from hours to weeks, and while no symptoms are present, changes are occurring in the internal organs. Following this asymptomatic period, other symptoms may appear. Loss of hair and appetite, fatigue, fever, severe diarrhea, vomiting, internal bleeding, and death may occur, depending on the dose received.

If a whole-body dose of 400-500 rem is received, approximately 50% of those exposed will die within 30 days if untreated. Recovery is likely with medical care although the exposed individual will suffer several months of illness. If the radiation dose is spread over several weeks, a person may survive a whole-body dose or large as 1000 to 2000 rem.

Exposure to a dose in excess of 700 rem to the entire body in a short period of time will likely result in death within a few weeks. This dose of radiation kills cells in the bone marrow and the body can no longer produce enough red blood cells to survive.

Cancer

Exposure to chronic small doses of radiation over long periods of time can result in delayed effects that may become apparent years after the initial exposure. Delayed effects may also occur after acute exposure to high doses. Delayed effects from exposure to ionizing radiation include carcinogenesis, life span shortening, and cataract formation.

The principle delayed effect from chronic exposure to radiation is an increased incidence of cancer. Ionizing radiation is a well known carcinogenic agent in animals and humans and has been implicated as capable of inducing all types of human cancers. Those types of cancer with the strongest association with radiation exposure include leukemia, cancer of the lung, bone, female breast, liver, skin, and thyroid gland.

By 1905 it was widely known that exposure to radiation could cause cancer. Many of the early researchers who were exposed to large repeated doses of radiation died from fatal skin cancer and leukemia. Marie and Pierre Curie, for example, both developed leukemia, probably from their experiments with radium.

Further evidences that ionizing radiation can induce cancer in humans has been demonstrated among radiation workers, children exposed in-utero to diagnostic x-rays, patients receiving therapeutic x-rays and internal radiation exposure, individuals exposed to fallout, and the Japanese A-bomb survivors. Some of these evidences are summarized below:

  1. Increased incidences of cancer have been noted among several groups of radiation workers exposed to high doses. Among these were the early radiologists, uranium miners, and radium watch dial painters. The early radiologists were often exposed to large doses of radiation without the benefit of protective devices. Many developed cancerous skin lesions on the hands and suffered from radiation burns. Higher incidences of leukemia were also demonstrated in this group. In the early 1900's, 50% of the uranium miners in some European mines died from lung cancer. Radium-dial painters at the beginning of this century, hand painted the luminous numerals on watches and clocks with a paint containing radium. The workers would put the brush on their lips to draw the bristles to a fine point. Increased incidences of bone cancer and other malignancies were seen in these workers.
  2. Increased incidences of cancer have been demonstrated from exposure to diagnostic x-rays. Children exposed to radiation as a result of abdominal x-rays to the mother during pregnancy have shown as increase in leukemia. An increase in breast cancer was noted among women with tuberculosis who received repeated fluoroscopic examinations.
  3. Exposure to therapeutic x-rays has resulted in increased incidences of cancer among patients treated for scalp ringworms, arthritis of the spine, and enlargement of the thymus glands. To reduce the size of the thymus gland, for example, doses of 120 to 6,000 rad were often given to infants. Increases were seen in thyroid cancer and leukemia.
  4. Mortality from liver cancer was increased among patients who received a radio-contrast material, Thorotrast. This compound contained thorium, a naturally occurring alpha emitting radioisotope.
  5. Increased incidences of thyroid cancer were demonstrated in residents of the Marshall Islands who were accidentally exposed to radioactive fallout from a nuclear bomb test. Children in Utah and Nevada exposed to fallout in the 1950's also demonstrated increases in thyroid cancer.
  6. The strongest evidence for radiation induced carcinogenesis in humans has come from studies of the Japanese A-bomb survivors. These data have suggested that radiation may be a general carcinogenic agent capable of inducing all types of cancers. Increased incidences of leukemia, cancer of the breast, respiratory organs, digestive organs, and urinary organs have been reported. In addition, the data has demonstrated a linear relationship between dose and radiation induced leukemia.

It is not known how radiation induces cancer. Several theories have been proposed to explain the carcinogenic properties of radiation. Cancer is characterized by the uncontrolled growth of cells in any tissue. According to one theory, radiation damages the chromosomes in the nucleus of a cell resulting in the abnormal replication of that cell. Another theory postulates that radiation decreases the overall resistance of the body and allows existing viruses to multiply and damage cells. A third theory suggests that as a result of irradiation of water molecules in the cells, highly reactive and damaging agents called "free radicals" are produced which may play a part in cancer formation.

Approximately 25% of all adults between the ages of 20 and 65 will develop cancer during their lifetime. It is not known what an individual's chances are of developing cancer from exposure to ionizing radiation. However, risk estimates can be made based on statistical increases in the incidence of cancer among populations exposed to large doses of radiation.

The Nuclear Regulatory Commission (NRC) has adopted a linear, non-threshold model for calculating the cancer risks associated with low level radiation exposure. According to the NRC, this model neither seriously underestimates nor overestimates the risks involved from radiation exposure. Using this model, the risks decrease proportionally to the does of radiation. Thus, a worker who receives 5,000 mR/yr is assumed to incur ten times the risk as a worker who receives 500 mR/yr. Because no threshold is assumed, theoretically all radiation exposures have the potential to cause cancer. Based on this model, the best risk estimates available today are that an additional 3 cancers would occur in a group of 10,000 radiation workers exposed to 1,000 mR each. This should be compared to the 2,500 cancer cases that would be expected to occur from other causes.

It is important to realize that these risk estimates are extrapolated from high doses and may not apply to low doses. Increases in cancer have not been clearly demonstrated at levels below the occupational limit of 5,000 mR/yr.

Recent controversial studies have suggested that linear extrapolation from high doses may significantly underestimate the actual risks involved from chronic low doses of radiation. Other studies have indicated that extrapolation may overestimate these risks. Both sets of data, however, lack sufficient validity to be used with confidence for the estimation of cancer risks at this time.

Genetic Effects

Radiation exposure to the reproductive cells can alter the genetic code, resulting in damaged or defective genes that can be passed on to future generations. It has been known since 1927 that radiation can cause genetic defects in the descendants of insects. Experiments with other animals have shown similar results. These studies demonstrated that radiation does not increase the types of mutations seen in nature, only the frequency.

Genetic mutations, however, have not been demonstrated in human populations exposed to radiation. For example, studies of the children of the A-bomb survivors in Japan have not detected any more genetic defects than expected. It is very difficult to determine if a person has a particular genetic defect. Usually there are no easily detectable signs and several generations and large populations may be necessary before the mutation becomes visible. Most effects will probably be seen in subsequent generations as minor impairments that lead to higher spontaneous abortions, shorter life spans, increases in diseases, and ill health. Serious genetic defects usually do not manifest themselves because the person does not survive to reproduce.

Based on the irradiation of animals, the following inferences can be made regarding genetic effects in humans:

  1. Radiation is a powerful mutagenic agent and any amount of radiation can potentially damage a reproductive cell.
  2. The vast majority of genetic mutations are recessive. Both a male and female must possess the same genetic alteration in their chromosomes in order for the mutation to be expressed.
  3. Most genetic mutations are harmful and decrease the overall biological fitness of a species.

Because genetic mutations are usually undesirable, the level of genetic defects in the population should be kept as low as possible. This can be accomplished by avoiding any unnecessary radiation exposure.

The risk of a genetic defect in a child of a person exposed to one rem of radiation is approximately one-third that of developing cancer. Thus, there would be about one chance in 10,000 that the child would have a genetic defect. Because genetic defects are less likely than cancer, and not as serious, the risk of developing cancer from radiation exposure is more significant.
 
Teratogenic Effects

Radiation exposure to a pregnant woman may be harmful to the unborn child. Malformations induced in the embryonic or fetal stages of development are termed teratogenic effects. Embryological and fetal tissue are composed of rapidly dividing unspecialized cells that are highly sensitive to damage from ionizing radiation. Radiation exposure in-utero can result in spontaneous abortions, congenital abnormalities, impairment of growth and mental functions, and increased incidences of leukemia.

The effects of radiation exposure during pregnancy are dependent on the stage of pregnancy and the dose of radiation received. The most critical stage of pregnancy is the first trimester. This includes the time a woman may not even be aware she is pregnant.

During this period, rapid cell division is occurring and the major body organs are forming. Exposure during the first trimester may result in embryonic death or congenital malformations. During the later stages of fetal growth, functional changes such as learning disorders or leukemia are possible. As the fetus ages, however, it becomes more resistant to radiation.

Evidences of embryological and fetal effects in humans have been demonstrated in the Japanese A-bomb survivors and children exposed to diagnostic x-rays while in-utero. An increase in mental retardation and small head circumference was observed in the children of the A-bomb survivors. Irradiation of the fetus from diagnostic x-rays has been associated with an increased incidence of leukemia in children. The highest risk occurred to those x-rayed during the first trimester. Because of the sensitivity of the developing fetus to radiation, a pregnant radiation worker should limit her whole-body exposure to 500 mR during the course of the pregnancy.

Conclusion

The health risks associated with exposure to ionizing radiation are smaller that the risks involved in many of our daily activities. These risks are also comparable to those encountered in other professions. This small but real increase in health risks calls for a weighing of the benefits versus the risks associated with the use of radiation. Radiation workers are benefited because their livelihood is derived from the use of radiation and students and researchers receive the benefit of a valuable educational and research tool. However, if the same information can be obtained by using methods that reduce the exposure and risks then they should be employed.

Because the biological effects of exposure to low level ionizing radiation are not fully understood, it is prudent to maintain radiation doses at a level that is as low as reasonably achievable (ALARA concept).

Laser Safety Program

1.0  Introduction

The term laser is an acronym for light amplification by the stimulated emission of radiation. The original concept for the laser was developed by Charles Townes in 1955, who won a Nobel Prize in 1964 for his work on the theory of lasers. The first laser was built by Theodore Maiman in 1960 using a synthetic ruby crystal as the lasing medium.

Lasers produce light by a process that involves changes in energy states within the atoms of certain materials. Atoms that have been promoted to higher energy states release this energy in the form of light by a process called stimulated emission. The laser light is amplified by reflecting it back and forth in the lasing medium with a pair of mirrors. The laser light is then released in a stream or pulse through a partially transmitting mirror at one end of the cavity.

Light emitted from a laser differs from normal light in several ways; it is extremely intense, coherent, monochromatic, and highly collimated. Wavelengths are typically released in the portion of the electromagnetic spectrum that extends through the ultraviolet, visible, and infrared regions.

Prior to the laser it was not possible to generate light with these characteristics. The unique properties of lasers have led to a number of applications in industry and construction where they are used to align, weld, cut, drill, heat, and measure distances. Lasers are also used in a variety of other fields including, medicine, communications, energy production, and national defense. Recently lasers are finding increased use in consumer products such as laser scanners, laser printers, and compact disk and video players.

2.0  Theory of Operation

Laser light is produced by changes in the energy levels of electrons. Under normal conditions electrons occupy the lowest energy state in an atom, known as the ground state. Electrons, however, can move from one energy level to another by the absorption or emission of energy.

Energy must be pumped into the system to excite the lasing material and promote electrons to higher energy states. Although electrons can absorb energy from a variety of external sources, two methods are most commonly used. The first occurs when the energy from a photon of light is absorbed by an electron. The laser may be optically pumped in this manner from sources such as flash lamps. The excess energy causes the electrons to jump to a higher energy level, resulting in a metastable state. Electrons absorb only those photons that contain the exact amount of energy needed to pump it to another energy level.

In gas lasers, electrons are pumped to higher energy states by a voltage generator. In this method, energy is supplied by collisions with electrons that have been accelerated to a specific energy. In addition to optical and electrical energy, some lasers are also pumped by chemical and nuclear energy.

Once in a higher energy state the atom can return to the ground state by releasing excess energy as a photon. The wavelength of light released is approximately equal to the energy difference between the excited and ground states. This release of a photon is called spontaneous emission.

Light emitted from phosphorescent materials is an example of spontaneous emission from a metastable state. These materials are excited to higher energy states by light from the sun or a lamp. Photons are released when the electrons drop to a lower energy level. Because the source of energy usually contains many wavelengths, the electrons can be excited to several energy levels. The released photons will be out of phase and composed of different wavelengths.

In 1917, Einstein theorized that a photon released from an excited atom could trigger another excited atom to release an identical photon. These two photons could trigger other atoms to release photons, resulting in an avalanche of photons. All of these photons would be of the same frequency, energy, direction, and in phase with the original triggering photon. This process is termed stimulated emission. The more atoms in an excited state, the greater the probability of stimulated emission. A population inversion occurs when the number of atoms in an excited state is greater than in the ground state.

The key component in making the laser operate properly is the optical cavity. The purpose of the optical cavity is to provide optimal amplification and stability for the laser beam. Most of the stimulated photons strike the walls of the optical cavity and are lost. However, those photons that are released in a direction parallel to the optical cavity can interact with other atoms causing further stimulated emissions. By placing mirrors at the end of the optical cavity, photons are reflected back and forth into the lasing medium; dramatically increasing the number of photons. The mirrors must be highly reflective and all scattering from other surfaces in the cavity must be kept low. In a typical laser, one mirror is flat with a reflectance greater than 99.9%. The other mirror is curved with a reflectance of 99% and a transmission of 1%. The beam emerges from the partially transmitting curved mirror. The lasing action will continue as long as energy is supplied to the lasing medium.

3.0  Lasing Medium

The lasing medium is a substance that can be stimulated to a metastable state by the addition of energy. The substance must be transparent to the light it produces and able to exist in a metastable state. The lasing medium may be solid, gaseous, dyes suspended in a liquid, or atoms or molecules doped into a crystalline structure.

Solid State

This type of laser contains a solid lasing medium embedded with atoms of the lasing material. Solid state lasers, because of a higher density of lasing atoms, can produce more power output per unit volume than gas lasers. They are usually pumped optically. Solid state lasers are usually simple to build and operate.

The first material used to make a laser was a synthetic ruby crystal. This crystal is made from aluminum oxide and a small amount of chromium oxide. The chromium is added as an impurity and acts as the active material in the laser. A xenon flashtube surrounds the crystal. One end of the rod-shaped crystal is silvered and the other end is partially silvered. A burst of light from the flashtube excites the chromium atoms and raises them to an excited state. This is defined as a population inversion. Some of the excited atoms release the excess energy in the form of light photons and return to the ground state. The photons travel between the reflecting ends of the rod and trigger other excited atoms through stimulated emission to release photons. An avalanche of photons results. This stream of photons is discharged through the partially mirrored end in a pulse of coherent light. The entire sequence takes only a few milliseconds.

Another example of a solid state laser is the Neodymium:YAG (yttrium aluminum garnet) laser. The neodymium is added as an impurity to the YAG crystal. The YAG laser is the most common type of crystal laser in use today. Like the ruby crystal, the YAG laser is pumped by a flash lamp. It can emit continuous beams or pulses. Continuous power outputs range from a few milliwatts to greater than 100 watts. Pulsed energies can result in power levels of 5,000 megawatts per pulse.

Neodymium can also be added to glass to make a neodymium-glass laser. This laser is similar to the YAG laser but is less expensive and does not conduct heat as well. Highly energetic pulses of light can be produced from the neodymium-glass laser. Peak powers of approximately one trillion watts can be generated in a pulse lasting only a nanosecond.

Gaseous

Many gases will lase and produce highly coherent light when an electric current is passed through them. The most common type of gaseous laser is the helium-neon. This laser is commonly used at construction sites, in teaching laboratories, and supermarkets.

The helium-neon laser is constructed of a long tube filled with helium and neon under low pressure. A few milliamps of direct current applied at several kilovolts is used to excite the helium atoms. The helium atoms in turn excite the neon atoms to a higher energy state by means of electron collisions and create a population inversion. Neon atoms fall to the ground state and release excess energy in the form of a light photon. Photons travels back and forth between the reflecting end mirrors and stimulate other neon atoms to release light photons. This results in a continuous stream of laser light known as a continuous wave. A bright beam of visible red light emerges from the exit mirror. The Helium-Neon laser can emit light continuously for thousands of hours. However, they are extremely inefficient, converting only 0.1% of the input energy to the laser beam.

Other examples of gaseous lasers include argon, krypton, and carbon dioxide lasers. Argon and krypton both emit a wide range of wavelengths, mostly in the visible region. The two gases can be mixed to generate most of the visible spectrum. Argon lasers are commonly used in industry and research and krypton-argon lasers are typically used in light shows. Helium-neon, argon, and krypton lasers all emit continuous beams.

The most powerful continuous wave laser is a carbon dioxide laser. It can continuously emit powers from less than a watt to hundreds of kilowatts. Carbon dioxide lasers can also produce extremely short pulses of even higher powers. The laser is pumped by an electrical discharge and emits invisible far-infrared light.

Carbon dioxide lasers operate slightly differently from other lasers. Instead of raising electrons to higher energy levels, the energy used to excite carbon dioxide atoms causes the atoms to vibrate at a different energy level. The carbon dioxide laser is widely used in industry to drill, cut, and weld materials because of its high power, high efficiency (up to 30% compared to 1% for neodymium lasers) and its ease of removing excess heat.

Excimer

The excimer laser is another example of a gaseous laser. An excimer is a molecule that can exist only in an electronically excited state. The excimer state does not exist in nature and exists for only a few nanoseconds in the laboratory. Electrons deposit energy in the laser gas causing an inert gas (argon, krypton, or xenon) to react with a halogen (chlorine, bromine, fluorine, or iodine) to form an excimer. The excimer then breaks up into its constituent atoms and releases the excess energy as light. These lasers are important because they can produce powerful pulses in the ultraviolet region. Excimer lasers are used in photochemistry and for marking silicon wafers used in electronic components.

Chemical Lasers

Gas lasers can also be energized strictly by chemical reactions that produce very high powered continuous wave or pulsed lasers. All chemical lasers emit infrared radiation. An example of this type of laser is the hydrogen fluoride laser. An atom of fluorine and hydrogen combine to produce hydrogen fluoride and energy. The molecules exist in a vibrationally excited state and the energy can be extracted in the form of a laser beam. Other examples of chemical lasers include iodine, hydrogen chloride, hydrogen bromide, deuterium fluoride, and carbon monoxide.

Dye Lasers

Many liquid organic dyes will lase if pumped with ultraviolet light. The dyes are dissolved in a liquid such as alcohol to form a solution. The energy levels of the dyes are spaced so close together that they form a continuum. This allows the dye molecules to release a wide range of wavelengths, mostly in the visible spectrum.

The most important characteristic of a dye laser is its tunability. A single wavelength in the dye's range can be selected for experimental purposes. Several dyes can be mixed to create a laser that can be tuned across the entire visible range. Dye lasers can also produce extremely short pulses on the order of a picosecond. They are usually very expensive, complex and are used primarily for research purposes.

Semiconductor Lasers

Lasing action can, under certain circumstances, be initiated by passing an electric current through a semiconductor. Semiconductor lasers, also known as diode lasers, are similar to light-emitting diodes (LED). These lasers are characterized by small size, small power, high efficiency, and long life. They are very simple, easy to use, and inexpensive.

In an LED, light is emitted by spontaneous emission. A diode laser, however operates predominantly through stimulated emissions. These devices are composed of tiny semiconductor crystals in which the end facets have been cut to reflect light. The diode laser is pumped by a high intensity electric current. A very small amount of light of a desired frequency is produced which stimulates an excited electron to fall to a lower energy state, giving off laser light.

Unlike other lasers, beam divergence is high, and output power is measured in microwatts. Semiconductor lasers are made chiefly from gallium-arsenide or gallium aluminum arsenide. These lasers are used in laser printers, video disks, audio disks, and fiber optics communication systems.

4.0  Mode of Operation

Lasers can operate in one of the following three modes:

  • continuous wave
  • pulsed
  • q-switching

Continuous Wave (CW)

Continuous wave lasers produce a steady stream of photons. Energy is pumped into the system at a rate that equals the light output. Beam characteristics are easily measured because the laser has reached a steady state condition. While most CW lasers use a gas medium, they can be constructed in a wide variety of lasing materials. An extensive array of wavelengths may be produced. The He-Ne laser was the first CW laser. Power levels can range from a few milliwatts for He-Ne lasers to several kilowatts for carbon dioxide lasers.

The output power in a continuous wave laser beam is measured in watts. The power density of a beam, also called irradiance or flux, is defined as watts per square centimeter. It is calculated from the output power of the beam and the beam diameter. Power densities can vary from a few watts to hundreds of watts per square centimeter.

Pulsed

These lasers release their energy in highly concentrated pulses of light. The pulse can be created by chopping a small portion of a continuous wave beam mechanically or electrically, or by pumping with short intense flashes of light. The energy is concentrated in small bursts delivered in 0.1 to 10 milliseconds per pulse. Pulsed lasers can damage biological tissues by mechanical blast interactions. Even low energies in the ocular focus region (0.4 to 1.4 um) can produce retinal damage. Pulsed beams can also be created by chemical means. Terms associated with pulsed beams are choppers, Q-switched, and mode locked. An example of a laser operating in the pulsed mode is the ruby laser.

The term used to evaluate a pulsed beam is output energy; measured in joules. The joule is equal to the power in watts multiplied by the time in seconds. The energy intensity or radiant exposure within a pulsed beam is expressed in joules per square centimeter.

Q-Switching

Extremely high power levels can be obtained by using a technique known as "q-switching" that momentarily stores excess energy. A shutter is placed in the optical path to prevent laser emission until a very large population inversion has built up. When the shutter is opened the electrons rapidly fall to the ground state releasing a tremendous pulse of energy that lasts only a few nanoseconds. Powers in the megawatt range can be produced by this technique. Q-switching is commonly used with ruby and neodymium solid lasers.

5.0  Characteristics of Lasers

The light from a laser differs from conventional light in four basic ways: 1) intensity, 2) coherence, 3) collimation, and 4) monochromaticity.

Intensity

Laser light contains a high concentration of energy per unit area of the beam. Lasers that emit only a few milliwatts of power can produce a highly intense beam 1-2 millimeters in diameter that will not diverge over a very long distance. Although lasers produce highly intense light, only a few types of lasers are truly powerful because intensity is defined as power per unit area. By comparison, an ordinary light bulb is more powerful than a typical laser, but the light is not collimated and consequently spreads out. For example, the light irradiance from a 1 mW He-Ne laser can be 6 orders of magnitude greater than that from a 100 W incandescent lamp at a distance of approximately 20 meters. Some lasers can produce thousands of watts continuously while others can produce trillions of watts in a nanosecond pulse.

Coherency

Ordinary light is incoherent or out of phase; light waves start at different times and move in all directions. Laser light, however, is coherent because it is the result of stimulated emission. All the waves produced by the laser are lined up or in phase with each other. The crests and troughs of each wave line up exactly and reinforce each other. The new light wave starts out exactly in phase with the photon that stimulated it. Holograms are based on this property of laser light.

Collimation

Because laser light is coherent it is highly collimated or directional. Laser beams are narrow, travel in virtually parallel lines, and will not spread out or diverge as light from most normal sources. Because of this small divergence the intensity of laser light, unlike ordinary light, is fairly constant over long distances. This property of lasers significantly increasing the hazard potential of the beam. The beam from a typical inexpensive laser will spread only about one meter after traveling one kilometer. Because laser beams are highly collimated they act as if they come from a distant point source. The beam can be easily focused to a small point by a simple lens, dramatically increasing the energy concentration of the beam. The property of collimation allows laser light to accurately measure distances, aim rifles, and track flying targets.

Reflections, however, reduce the collimation of the laser beam and result in beam divergence. Laser beams are reflected to some extent from all surfaces. If the reflecting surface is mirror-like, the reflection is termed specular. The reflection is called diffuse if the reflecting surface is rough. The spreading is greater when the reflection is from a rough or diffuse spreading surface. Beam intensity can be reduced by a factor of hundreds to thousands. The roughness of the diffuse reflector is more important than the color in reducing intensities.

Monochromaticity

Unlike ordinary light, which is composed of all the colors of the spectrum, laser light is composed of only one color. All the light waves in the beam are composed of the same wavelength. Each laser produces its own characteristic color of light.

Some lasers are tunable and can be adjusted to produce several different colors, but they can emit only one color at a time. Because laser light is monochromatic it can be used to selectively interact with materials, revealing information about the structure of atoms and molecules. Laser light is approximately 10 million times more monochromatic than conventional light sources.

6.0  Biological Effects

The eye is extremely vulnerable to injury if exposed to the beams from most types of lasers. The type of injury depends upon the intensity of light, its wavelength, and the tissue exposed. Damage results from either temperature or photochemical effects. Acute exposure may result in corneal or retinal burns. Cataract formation or damage to the retina may result from chronic exposure to laser light. Retinal damage is of particular concern from exposure to wavelengths in the visible and near infrared region.

Most sources of incoherent light can be viewed safely because the light reaching the eye is only a small portion of the total output and the energy is spread over the entire retina. Laser radiation, however, is composed of coherent light. The beam can pass through the pupil and focus on a very small spot on the retina, depositing all its energy on this area. Only visible and near infrared radiation is focused on the retina. Damage to the retina may result in limited or total blindness if the optic nerve is injured. Injury may be irreversible and there may be no pain or discomfort from the exposure.

In addition to heat damage, some very high-powered, short-pulsed lasers such as the carbon dioxide and the Nd YAG mode-locked laser can cause shock waves that can mechanically disrupt the retina and cause the eye to hemorrhage.

Damage to the skin is also possible from exposure to laser beams. Acute exposure may cause injuries ranging from mild reddening to blistering and charring. Skin cancers may result from chronic exposure to ultraviolet light. The extent and type of damage depends on the amount of energy deposited and the wavelength of the light. Unlike injury to the eye, acute damage to the skin is usually repairable.

Ultraviolet radiation (200-400 nanometers)

Exposure to the eye from ultraviolet light in the 200 nm to 315 nm range is absorbed by the cornea and may cause photokeratitis (corneal inflammation). Unlike the skin, repeated exposure of the cornea to ultraviolet light does not result in a protective mechanism. Near ultraviolet light between 315 nm and 400 nm is absorbed largely in the lens and may cause cataracts. Wavelengths less than 400 nm do not pose a hazard to the retina.

Exposure to the skin from lasers that emit in the UV region may cause a photochemical reaction resulting in reddening, aging, and possibly skin cancer. Examples of lasers operating in the ultraviolet region include the neodymium:YAG-Quadrupled (QSW & CW), and the Ruby (doubled) laser.

Visible and Near-Infrared Radiation (400 to 1400 nanometers)

Exposure to laser beams in the visible (400 nm - 700 nm) and near-infrared (700 nm - 1400 nm) regions of the spectrum may damage the retina. Laser beams in this region are readily transmitted by the eye and focused by the lens to produce an intense concentration of light energy on the retina. The incident exposure on the cornea can be concentrated by a factor of approximately 100,000 times at the retina due to this focusing effect. This energy is converted to heat and may cause a retinal burn resulting in visual loss or even blindness if the optic nerve is injured. Even low energy laser beams, if concentrated by a factor of 100,000, can cause damage to the eye. For this reason wavelengths in the 400 nm to 1400 nm range are termed the ocular hazard region.

Exposure to the skin from laser beams in the visible and infrared regions may cause photosensitive reactions, skin burns and excessive dry skin. Lasers operating in the visible region of the spectrum include the ruby, neodymium:YAG (doubled), helium-cadmium, helium-neon, argon, and krypton. Lasers operating in the near-infrared region include the neodymium:YAG, gallium arsenide, and helium-neon.

Middle and Far-Infrared Radiation (1,400 -10,000 nanometers)

Laser beams in the middle and far-infrared regions produce injury primarily to the cornea and to a lesser extent the lens. Damage is usually from heating effects, although pulsed lasers such as the carbon dioxide laser may cause injury from thermomechanical effects. Virtually no light reaches the retina beyond 1400 nm. Middle-infrared radiation between 1,400 nm and 3,000 nm may penetrate deep into the lens causing cataracts. Far-infrared radiation in the 3000 nm to 10,000 nm range is absorbed by the cornea and may cause corneal burns and loss of vision.

The major danger to the skin from lasers operating in this region is burn damage. Lasers operating in this region include: hydrogen fluoride, carbon monoxide, carbon dioxide, and hydrogen cyanide.

7.0  Laser Safety Standards

Laser safety standards are derived from government mandated regulations and voluntary standards. Safety rules governing the manufacture of lasers are established by the Federal Government. Laser products manufactured after August 2, 1976 must conform to performance standards established by the Food and Drug Administration (FDA), (21 CFR 1040.10). The standard requires that lasers be properly classified and labeled by the manufacturer. Thus, for most lasers, measurements or calculations to determine the hazard classification are not necessary. In addition, the standard establishes certain engineering requirements for each class and requires warning labels that state maximum output power. Although the performance standard regulates the manufacture of lasers it does not address the safe use of lasers.

OSHA Regulations (29 CFR 1926.54 and 102) specify generalized rules for the safe use of lasers in the construction industry. These include user training, posting and labeling requirements, laser safety goggles, and maximum exposure intensities. Requirements for the use of laser goggles in general industry are specified in sections 1910.132-133. The safe use of lasers in general industry (including research laboratories) is covered under OSHAs General Duty Clause which states that employers must furnish employees a place of employment that is free from recognized hazards that are likely to cause death or serious injury.

Extensive recommendations for the safe use of lasers have been developed by the American National Standards Institute (ANSI) and adopted by the American Conference for Governmental Industrial Hygienists (ACGIH). Lasers are classified according to their relative hazards, and appropriate control measures for each class are specified. Compliance with these standards generally eliminates the need for measurement of laser radiation, quantitative analysis of hazard potential, or use of the Threshold Limit Value (TLV). Compliance with ANSI and OSHAs Construction Standard will usually satisfy the requirements of the OSHA General Duty Clause.

8.0  Laser Classification

Since August, 1976 manufacturer's have been required by Federal law to classify lasers. If the class is not known, it can be determined by measurements and/or calculations. Lasers are classified according to the ability of the primary or reflected beam to injure the eye or skin. The appropriate class is determined from the wavelength, power output, and duration of pulse (if pulsed). Classification is based on the maximum accessible output power. There are four laser classes, with Class 1 representing the least hazardous. All lasers, except Class 1, must be labeled with the appropriate hazard classification.

Class 1

Class 1 laser devices cannot produce damaging radiation levels to the eye even if viewed accidentally. Prolonged staring at the laser beam however, should be avoided as a matter of good practice. This class has a power output less than 0.4 uW for CW lasers operating in the visible range. A completely enclosed laser of a higher classification is categorized as a Class 1 laser if emissions from the enclosure cannot exceed Class 1 limits. If the enclosure is removed, e.g. during repair, control measures for the class of laser contained within are required.

Class 2

Class 2 lasers are incapable of causing eye injury within the duration of the blink, or aversion response (0.25 sec). Although these lasers cannot cause eye injury under normal circumstances, they can produce injury if viewed directly for extended periods of time. Class 2 lasers only operate in the visible range (400 nm to 700 nm) and have power outputs between 0.4 uW and 1 mW for CW lasers. The majority of Class 2 lasers are helium-neon devices.

Class 3a

Class 3a lasers cannot damage the eye within the duration of the blink or aversion response. However, injury is possible if the beam is viewed through binoculars or similar optical devices, or by staring at the direct beam. Power outputs for CW lasers operating in the visible range are between 1 mW and 5 mW.

Class 3b

Class 3b lasers can produce accidental injuries to the eye from viewing the direct beam or a specularly reflected beam. Class 3b laser power outputs are between 5 mW and 500 mW for CW lasers. Except for higher power Class 3b lasers, this class will not produce a hazardous diffuse reflection unless viewed through an optical instrument.

Class 4

Class 4 lasers are the most hazardous lasers. Exposure to the primary beam, specular reflections, and diffuse reflections are potentially hazardous to the skin and eyes. In addition, class 4 lasers can ignite flammable targets, create hazardous airborne contaminants and usually contain a potentially lethal high voltage supply. The power output for CW lasers operating in all wavelength ranges is greater than 500 mW. All pulsed lasers operating in the ocular focus region (400 nm to 1400 nm) should be considered Class 4.

Unknown Class

Laser classification can be determined by measuring the output irradiance or radiant exposure using instruments traceable to the National Bureau of Standards. These measurements should only be performed by qualified personnel. The laser class can also be determined from calculations. For CW lasers, the wavelength and average power output must be known. Classification of pulsed lasers requires the following information: wavelength, total energy per pulse (or peak power), pulse duration, pulse repetition frequency (PRF), and emergent beam radiant exposure. In addition to the above information laser source radiance and maximum viewing angle subtended by the laser must be known for extended-source lasers, such as injection laser diodes. Detailed information on classifying lasers may be found in the ANSI Guide for the Safe Use of Lasers.

9.0  Control Measures for Laser Radiation

The recommended procedure for using lasers safely is to identify the class involved and then comply with the appropriate control measures. Control measures are designed to reduce the possibility of exposure to the eye and skin from hazardous laser radiation. Preventing ocular exposure from the primary beam and specular reflections is of primary concern because serious injury to the unprotected eye is possible.

To control potential hazards, priority should be given to the use of engineering controls. Although commercial laser products manufactured after August 2, 1976 incorporate many engineering controls, the use of additional controls should be considered to reduce the risks.The most effective engineering control is to totally enclose the laser and all beam paths.

The potential for exposure to hazardous laser radiation is probably greatest in the research laboratory where open and high power laser beams are frequently encountered. Because researchers need flexibility to change optical arrangements and make adjustments during experimental procedures, laser beams cannot always be totally enclosed. Generally in research laboratories where engineering controls cannot be relied upon, administrative controls, protective eyewear, and properly supervised laser controlled areas must be rigorously enforced to reduce hazards.

Because OSHA standards are generally non-specific, users are encouraged to adopt the following requirements and recommendations for the safe use of lasers. These practices are based on the FDA Performance Standard, OSHA Regulations, and the ANSI Hazard Classification System. Engineering controls specified by the FDA Performance Standard apply only to manufacturers of laser equipment but should be incorporated by users when practical.

Protective Housing (All Classes-FDA)- A protective housing shall be provided by the manufacturer to prevent access to laser radiation which exceeds the intended classification. If the protective housing is removed, as in research laboratories, control measures shall be based on the maximum accessible radiation.

Safety Interlock (All Classes-FDA)- Any portion of the protective housing designed to be removed without tools shall be interlocked to prevent access to radiation in excess of the applicable class.

Optical Viewing Devices and Windows (All Classes)- Viewing optics (including lenses, telescopes, microscopes, and viewing windows) shall not be used to view the direct beam or specular reflections unless an appropriate filter is used or adequate laser protective eyewear is worn to reduce laser radiation to safe levels.

Maximum Exposure (All Classes)- Workers shall not be exposed to light intensities above:

  • Direct Staring: 1 microwatt per square centimeter
  • Incidental Observing: 1 milliwatt per square centimeter
  • Diffused Reflected Light: 2.5 watts per square centimeter

Directing beam at people (All Classes)- The laser beam shall not be directed at people or into potentially occupied areas. Experiments should be designed so that the laser beam is not at eye level.

Registration (Classes 3a, 3b, 4)- These lasers shall be registered with the Radiation Safety Office.

Reduction of Intensities (Class 2, 3a, 3b, 4)- If full output power is not needed, the laser beam intensity should be reduced to a less hazardous level by using absorbing filters or beam shutters.

Alignment (Class 2, 3a, 3b, 4)- Alignment of laser optical components (mirrors, lenses, beam deflectors, etc.) shall be done in a manner that ensures the eyes are not exposed to hazardous levels of radiation.

Firm Laser Mount (Class 2, 3a, 3b, 4)- The laser should be mounted on a firm support to ensure that the beam travels along its intended path.

Unattended Operation (Class 2, 3a, 3b, 4)- Operating lasers should not be left unattended for appreciable lengths of time. Lasers should be turned off, or beam shutters or caps should be used when laser transmission is not required.

Emission Indicator (Class 2, 3a, 3b, 4-FDA)- Laser systems shall incorporate an emission indicator that provides a visible or audible signal during radiation emission.

Safety Eyewear (Class 2, 3a, 3b, 4)- Laser eyewear designed to protect for the specific wavelengths of the laser shall be worn when exposure to hazardous levels of laser radiation are possible. Laser safety eyewear shall be worn in areas where unenclosed Class 3b or 4 lasers are operated. The optical density of the eyewear shall reduce the laser radiation to the eye to safe levels. Safety eyewear shall be labeled with the optical density of the lens and the wavelength that it protects against.

Beam Stop or Attenuator (Class 3a, 3b, 4)- Potentially hazardous beams should be terminated by a permanently attached beam stop or attenuator. The beam stop should be non-reflecting and fire-retardant.

Training (Class 3a, 3b, 4)- Personnel shall receive training in basic laser safety procedures. Training should include the potential hazards associated with the use of the laser and control measures necessary to minimize exposure to laser radiation. Training should be an on-going program, both for new employees and experienced personnel, and when new equipment is used. Written standard operating procedures, and a training manual should be presented to each individual assigned to work with a Class 3 or 4 laser. Documentation of training should be readily available.

Medical Surveillance (Class 3b, 4)- Personnel operating Class 3b and 4 lasers should receive appropriate eye and skin examinations prior to laser use. Examinations should be repeated every three years.

Remote Interlock Connector (Class 3b, 4-FDA)- A remote interlock connector shall be provided to allow electrical connections to an emergency disconnect interlock or a door interlock.

Spectators (Class 3b, 4)- Spectators should not be allowed in a laser controlled area containing an unenclosed Class 3b or 4 laser unless permission has been obtained from the supervisor, potential hazards have been explained, and appropriate protective measures taken.

Beam shutters (Class 3b, 4)- Lasers should be equipped with a beam shutter that covers the aperture. The shutter should completely stop the laser beam. A black, non-reflective material is desirable.

Warning System (Class 3b, 4)- A visible or audible warning device that activates prior to laser emission should be provided. The delay time should be sufficient to allow personnel to avoid exposure to the beam.

Key-Switch (Class 3b, 4-FDA)
- Class 3b and 4 lasers shall be provided with a keyed switching device. The key shall be removable and the laser shall be inoperable once the key has been removed.

Enclosed Beam Path (Class 3b, 4)- The entire beam path, including the target area, should be enclosed if possible. Safety interlocks should be used with the enclosure. If the beam is enclosed the laser could revert to a less hazardous laser classification.

Laser Controlled Area (Class 3b)- Unenclosed Class 3b laser systems should be operated in a controlled area.

  1. The laser controlled area should be under the direct supervision of an individual knowledgeable in laser equipment and trained in laser safety procedures.
  2. Spectators should be prevented from entering the laser area during the operation of the laser.
  3. The area shall be posted with appropriate laser warning signs.
  4. Specular surfaces should be removed from the beam path, if possible. If removal is not possible the surfaces should be painted a flat-black color or covered with a diffuse material. The intended target should be a diffuse, absorbing material to prevent reflections.
  5. To reduce the possibility of specular reflections personnel should not wear watches or jewelry in controlled areas.
  6. Appropriate eye protection shall be worn by all personnel potentially exposed to hazardous levels of radiation.

    Laser Controlled Area (Class 4)- Unenclosed Class 4 lasers shall be restricted to a well controlled area suitably administered and designed to protect personnel from exposure to laser radiation. The following requirements are in addition to those for a Class 3b controlled area:

  7. Access to the controlled area shall be restricted to authorized personnel during the operation of the laser.
  8. Doors to the laser controlled area shall be provided with safety interlocks or a guard must be posted to prevent unexpected entry during laser operation.
  9. A warning light connected to the power supply or shutter must be installed on doors leading to the laser facility.
  10. A "panic switch" should be readily available for deactivating the laser during an emergency.
  11. The work area shall be separated from the surrounding environment by walls, panels, or black flameproof heavy curtains.
  12. The laser controlled area must be posted with the appropriate warning sign and a notice that protective eyewear must be worn before entering the restricted area.
  13. The facility should be light tight. Windows and other openings should be covered to prevent the transmission of hazardous laser radiation to potentially occupied areas.
  14. If possible, Class 4 lasers should be operated by remote control and monitored by television.
  15. Walls in the laser laboratory should be dark, dull, and non- reflecting.

10.0  Labels

Warning signs and labels shall be in accordance with the FDA Performance Standard and ANSI Standards. Signs and labels shall be conspicuously displayed on equipment and on access doors where applicable. Additional precautionary instructions, such as eye protection required, should be included on the sign or label.

Class 1:  Warning labels and signs are not required for Class 1 lasers. Enclosed Class I lasers containing more hazardous laser radiation within shall have a warning label located on the access panel.

Class 2:  The label must include the laser hazard symbol and the words "CAUTION- Laser Radiation- Do Not Stare into Beam", the class, and type of laser. Warning signs on doors are not required.

Class 3a:  Signs and labels shall include the laser hazard symbol and bear the words "CAUTION- Laser Radiation- Do Not Stare into Beam or View Directly with Optical Instruments ", the class, and type of laser. Entrances to laser areas should be posted with a warning sign.

Class 3b:  Signs and labels shall include the laser hazard symbol and bear the words "DANGER- Laser Radiation- Avoid Direct Exposure to Beam", the class, and type of laser. Doors leading to the laser area shall be posted with warning signs.

Class 4:  Appropriate warning signs must be posted on equipment and doors leading to the facility. Signs and labels shall include the laser hazard symbol and bear the words "Danger- Laser Radiation- Avoid Eye or Skin Exposure to Direct or Scattered Radiation", the class, and type of laser. Additional precautions or protective actions should be provided as needed.

11.0  Invisible Radiation

Because infrared and ultraviolet radiation are invisible, special precautions must be used when working with lasers that emit radiations in these regions. Labels and warning signs should specify that lasers produce invisible radiation. In addition to the above requirements, the following recommendations should be used when working with infrared or ultraviolet lasers:

Infrared:  For Class 3 & 4 lasers, the beam path should be terminated with a highly absorbent, non-reflecting backstop. Caution should be used because metal surfaces that appear dull can cause specular reflections of infrared radiations. In addition, for Class 4 lasers, the beam path should be terminated by a fire resistant backstop such as firebrick. The backstop should be inspected periodically for degradation. The beam and target area should be shielded with infrared absorbing materials, such as lucite or plexiglass, to minimize reflections from Class 3b or Class 4 lasers.

Ultraviolet:  Exposure to ultraviolet radiation should be minimized by using materials that attenuate the radiation to safe levels. Special attention should be given to the possibility of producing undesirable reactions in the presence of ultraviolet radiation, e.g. ozone.

12.0  Associated Hazards

In addition to the hazards of the laser beam, protection is also necessary from other hazards associated with the operation of the laser. These hazards include explosions, electrical shocks, cryogenic liquids, flammable liquids, noise, x-rays, UV radiation, and airborne contaminants.

Explosion Hazards

Lasers and ancillary equipment may present explosion hazards. High pressure arc lamps and filament lamps used to excite the lasing medium should be enclosed in housings that can withstand an explosion if the lamp disintegrates. In addition, the laser target and elements of the optical train may shatter during laser operation and should be enclosed in a suitable protective housing. Capacitors may explode if subjected to voltages higher than their rating and should be adequately contained. High energy capacitors should be enclosed in one-eighth inch thick steel cabinets.

Electrical Hazards

Lethal electrical hazards may be present, especially around high power laser systems. Continuous wave lasers use direct current or radiofrequency power supplies and pulsed lasers employ large capacitor banks for electrical storage. Lasers and associated electrical equipment should be designed, constructed, installed and maintained in accordance with the American National Standard Electrical Code. Electrical circuits greater than 42.5 volts are considered hazardous unless limited to less than 0.5 mA.

To reduce electrical hazards high voltage sources and terminals should be enclosed. Power should be turned off and all high-voltage points grounded before working on power supplies. Operators should not stand on metal floors, or in water while working with live electronic equipment. Accessible, non-current carrying metallic parts of laser equipment must be grounded. Electrical circuits should be evaluated with respect to fire hazards.

Cryogenics

Cryogenic liquids (especially liquid nitrogen) may be used to cool the laser crystal and associated receiving and transmitting equipment. These liquified gases are capable of producing skin burns and may replace the oxygen in small unventilated rooms. The storage and handling of cryogenic liquids should be performed in a safe manner. Insulated handling gloves of quick removal type should be worn. Clothing should have no pockets or cuffs to catch spilled cryogenics. Suitable eye protection should be worn. If a spill occurs on the skin, the area should be flooded with large quantities of water. Adequate ventilation should be present in areas where cryogenic liquids are used.

Flammable Hazards

Flammable solvents, gases, and combustible materials may be ignited by a Class 4 laser beam. Laser beams should be terminated by a non-combustible material such as a brick. Combustible solvents or materials should be stored in proper containers, and shielded from the laser beam or electrical sparks. Lasers and laser facilities should be constructed and operated to eliminate or reduce any fire hazard. Unnecessary combustible materials should be removed in order to minimize fire hazards. Laser laboratories should contain an appropriate fire extinguisher.

Noise

Noise levels in laser laboratories can exceed safe limits because of high voltage capacitor discharges. Hearing protection may be required.

X-Rays

X-ray production is possible when high voltages exceed 15 kV. Although most laser systems use voltages less than 8 kV, some research models may operate above 20 kV. Laser systems capable of producing ionizing radiation must be surveyed by the Safety Office to ensure that x-ray levels are within legal limits.

Ultraviolet Radiation

Although laser radiation presents the chief hazard, it may not be the only optical hazard. Laser discharge tubes and pumping tubes may emit hazardous levels of ultraviolet radiation and should be suitably shielded. Particular care should be used with quartz tubes. Most lasers now use heat-resistant glass discharge tubes which are opaque in the UV-B (280 nm-315 nm) and UV-C (100 nm-280 nm) spectrum.

Chemical Hazards

Vaporized target materials, toxic gases, vapors and fumes may be present in a laser area. Ozone is produced around flash lamps and concentrations of ozone can build up with high repetition rate lasers. Asbestos fibers may be released from the firebrick used as backstops for carbon dioxide lasers.

The increasing use of chemical lasers may introduce chemical hazards that are more dangerous than the laser radiation. For example, fluorides used in fluoride lasers are highly toxic and demand immediate emergency measures upon contact. He-Cd lasers may contaminate the laboratory with toxic cadmium vapors if the exhaust gases are not vented to the outside. The dyes that are the active medium of tunable lasers are often very toxic and may cause acute or chronic skin problems. Some dyes may be carcinogenic. Gloves, laboratory coats, and proper eye protection must be worn when handling hazardous chemicals. An eyewash station and emergency shower shall be available in areas where there is a possibility that hazardous chemicals may be splashed in the eyes or on the skin. Food or drink should not be consumed in the laser lab if potential toxic air contaminants or chemicals are present. Adequate general ventilation or local exhaust must be maintained in laser installations to ensure that toxic air contaminants are below acceptable limits.

13.0  Threshold Limit Value

The Threshold Limit Value (TLV) is the amount of laser radiation that nearly all individuals may be exposed to without experiencing adverse effects. TLVs have been developed for exposure to the eye and skin. TLVs for the eye are based on possible exposure to the direct beam or from extended diffuse reflections. No person shall operate a laser in a manner that exposes the unprotected eye or skin to laser radiation in excess of the applicable TLV. If engineering controls are not suitable to reduce levels below the TLV then laser safety eyewear must be worn.

If the laser classification is known it is generally unnecessary to perform calculations or monitor the laser environment to determine if exposure of the eyes or skin is dangerous. Appropriate control measures for the classification should be implemented. For example, if a class 3b or 4 laser is used, the TLV for the eyes may be exceeded from viewing the direct or specular beam and appropriate eye protection must be worn. Because only Class 4 lasers can produce hazardous diffuse reflections, calculations for viewing diffuse reflections from class 1, 2, and 3 systems are not necessary.

The TLV should be determined if the laser has not been classified by the manufacturer and a quantitative evaluation of the hazard associated with a laser is needed. Monitoring is often improperly performed and has a high degree of error. Calculations should be used in most situations to determine if exposures are below the applicable TLV. The ANSI Guide for the Safe Use of Lasers should be consulted to calculate TLVs and the latest edition of the ACGIH Threshold Limit Values should be consulted for current TLVs (available from the Safety Office). Irradiance and radiant exposure are used to describe exposure limits from direct laser sources. Exposure limits from extended sources are described in radiance and time-integrated radiance.

14.0  Laser Safety Eyewear

The energy emitted from lasers is highly concentrated and can cause permanent eye injury. Although engineering controls are preferred to reduce hazards from the laser beam, it may be necessary to use laser safety eyewear when engineering controls are inadequate. The eyewear should be matched to the wavelength emitted and provide proper attenuation for the laser intensity. Laser safety eyewear must be clearly marked with the optical density of the lens and wavelengths for which protection is provided. The following factors should be considered when purchasing laser protective eyewear:

Wavelength:  The wavelength of the laser output must be known. If the laser emits more than one wavelength, each wavelength must be considered.

Optical Density:  The attenuation of laser light by protective goggles is given by its optical density (OD). The OD must be sufficient to reduce the laser light to safe levels while transmitting sufficient ambient light for safe visibility. The OD is measured on a logarithmic scale, thus a filter that attenuates a beam by a factor of 1,000 has an OD of 3 and a filter with an OD of 6 attenuates the beam by a factor of 1,000,000. The required OD is determined from the maximum intensity that an individual could be exposed.

Laser Beam Intensity:  The maximum irradiance in watts/square centimeter for CW lasers and the maximum radiant exposure in joules/square centimeter for pulsed lasers must be known.

Luminous Transmittance:  When considering laser safety goggles the visible or luminous transmission must be considered along with the optical density. Luminous transmission is given in percent transmission of visible light. Laser goggles with a lower luminous transmittance than required may result in eye fatigue and accidents. However, proper optical density should not be sacrificed for increased luminous transmission.

Damage Threshold: The resistance of the lenses to damage from the laser beam must be considered. The damage can take the form of bubbling, melting, or shattering. The lens must be capable of absorbing the amount of energy under the most severe operating conditions without suffering changes in the light transmission characteristics. Laser goggles should be inspected periodically for pitting, cracking, discoloration and deterioration in the mountings.

Comfort:  Laser safety eyewear should be comfortable and provide a good fit. Spectacle type frames generally are more comfortable than goggles but do not fit as tight and may allow unattenuated laser radiation to reach the eyes. However, the increased comfort of spectacle type frames may increase user acceptance.

Lenses: Lenses in laser safety eyewear can be made of reflective glass or plastic, absorptive glass filters, or absorptive polymeric filters. Reflective lenses can create potentially hazardous specular reflections. These lenses are also heavy and uncomfortable and can scratch easily, allowing potentially hazardous radiation to reach the eye. Absorptive filters are not affected by surface scratches nor do they create potentially hazardous reflections. Polymeric filters, such as polycarbonate, offer several advantages over glass absorptive filters. They are lighter, have better impact resistance, and can withstand higher energy densities. Lenses should be mounted in goggle type frames to ensure maximum protection. No lens material is useful for all wavelengths and for all radiant exposures.

15.0  Medical Surveillance

Personnel who routinely use Class 3b or Class 4 lasers should be enrolled in the Medical Surveillance Program for examination of the eyes and skin. The examination should include a medical history, with emphasis on the eyes and skin. Current and past medication usage should be reviewed, particularly the use of photosensitizing drugs. Visual acuity should be determined and the structures of the eye that could be injured from the wavelengths emitted should be examined. For example, workers using laser systems operating in the wavelength range of 400 to 1400 nm should have retinal examinations. Employees working with ultraviolet lasers or who have a history of photosensitivity should have skin examinations. Workers who only occasionally use Class 3b or 4 lasers should have a visual acuity test.

Medical examinations should be performed prior to employment and following any suspected laser injury. Eye examinations should be repeated every three years to detect injury or subtle changes that may have occurred from chronic exposure.

NRC FORM 3
(8-1999)

UNITED STATES NUCLEAR REGULATORY COMMISSION
Washington, DC 20555-0001

NOTICE TO EMPLOYEES

STANDARDS FOR PROTECTION AGAINST RADIATION (PART 20); NOTICES,
INSTRUCTIONS AND REPORTS TO WORKERS; INSPECTIONS (PART 19); EMPLOYEE PROTECTION

WHAT IS THE NUCLEAR REGULATORY COMMISSION?

The Nuclear Regulatory Commission is an independent Federal regulatory agency responsible for licensing and inspecting nuclear power plants and other commercial uses of radioactive materials.

WHAT DOES THE NRC DO?

The NRC=s primary responsibility is to ensure that workers and the public are protected from unnecessary or excessive exposure to radiation and that nuclear facilities, including power plants, are constructed to high quality standards and operated in a safe manner. The NRC does this by establishing requirements in Title 10 of the Code of Federal Regulations (10 CAR) and in licenses issued to nuclear users.

WHAT RESPONSIBILITY DOES MY EMPLOYER HAVE?

Any company that conducts activities by the NRC must comply with the NRC=s requirements. If a company violates NRC requirements, it can be fined or have it=s license modified, suspended or revoked.

Your employer must tell you which NRC radiation requirements apply to your work and must post NRC Notices of Violation involving radiological working conditions.

WHAT IS MY RESPONSIBILITY?

For your own protection and the protection of your co-workers, you should know how NRC requirements relate to your work and should obey them. If you observe violations of the requirements or have a safety concern, you should report them.

WHAT IF I CAUSE A VIOLATION?

If you engaged in deliberate misconduct that may cause a violation of the NRC requirements, or would have caused a violation if it had not been detected, or deliberately provided inaccurate or incomplete information to either the NRC or to your employer, you may be subject to enforcement action. If you report such a violation, the NRC will consider the circumstances surrounding your reporting in determining the appropriate enforcement action, if any.

HOW DO I REPORT VIOLATIONS AND SAFETY CONCERN?

If you believe that violations of NRC rules or the terms of the license have occurred, or if you have a safety concern, you should report them immediately to your supervisor. You may report violations or safety concerns directly to the NRC. However, the NRC encourages you to raise your concerns with the licensee since it is the licensee who has the primary responsibility for, and is most able to ensure, safe operation of nuclear facilities. If you choose to report your concern directly to the NRC, you may report this to an NRC inspector or call or write to the NRC Regional Office serving your area. If you send your concern in writing, it will assist the NRC in protecting your identity if you clearly state in the beginning of your letter that you have a safety concern or that you are submitting an allegation. The NRC=s toll-free SAFETY HOTLINE for reporting safety concerns is listed below. The addresses for the NRC Regional Offices and the toll-free telephone numbers are also listed below.

WHAT IF I WORK WITH RADIOACTIVE MATERIAL OR IN THE VICINITY OF A RADIOACTIVE SOURCE?

If you work with radioactive materials or near a radiation source, the amount of radiation exposure that you are permitted to receive may be limited by NRC regulations. The limits on your exposure are contained in section 20.1201, 20.1207, and 20.1208 of Title 10 of the Code of Federal Regulations (10 CAR 20) depending on the part of the regulations to which your employer is subject. While these are the maximum allowable limits, your employer should also keep your radiation exposure as far below those limits as Areasonably achievable.@

MAY I GET A RECORD OF MY RADIATION EXPOSURE?

Yes. Your employer is required to advise you of your dose annually if you are exposed to radiation for which monitoring was required by NRC. In addition, you may request a written report of your exposure when you leave your job.

HOW ARE VIOLATIONS OF NRC REQUIREMENTS IDENTIFIED?

NRC conducts regular inspections at licensed facilities to assure compliance with NRC requirements. In addition, your employer and site contractors conduct their own inspections to assure compliance. All inspectors are protected by Federal law. Interference with them may result in criminal prosecution for a Federal offense.

MAY I TALK WITH AN NRC INSPECTOR?

Yes. NRC inspectors want to talk to you if you are worried about radiation safety or have other safety concerns about licensed activities, such as the quality of construction or operations at your facility. Your employer may not prevent you from talking with an inspector. The NRC will make all reasonable efforts to protect your identity where appropriate and possible.

MAY I REQUEST AN INSPECTION?

Yes. If you believe that your employer has not corrected violations involving radiological working conditions, you may request an inspection. Your request should be addressed to the nearest NRC Regional Office and must describe the alleged violation in detail. It must be signed by you or your representative.

HOW DO I CONTACT THE NRC?

Talk to an NRC inspector on-site or call or write to the nearest NRC Regional Office in your geographical area . If you call the NRC=s toll-free SAFETY HOTLINE during normal business hours, your call will automatically be directed to the NRC Regional Office for your geographical area. If you call after normal business hours, your call will be directed to the NRC=s headquarters Operations Center, which is manned 24 hours a day.

CAN I BE FIRED FOR RAISING A SAFETY CONCERN?

Federal law prohibits an employer from firing or otherwise discriminating against you for bringing safety concerns to the attention of your employer or the NRC. You may not be fired or discriminated against because you:

  • Ask the NRC to enforce its rules against your employer.
  • Refuse to engage in activities which violate NRC requirements.
  • Provide information or are about to provide information to the NRC or your employer about violations of requirements or safety concerns.
  • Are about to ask for, or testify, help, or take part in an NRC, Congressional, or any Federal or State proceeding.

WHAT FORMS OF DISCRIMINATION ARE PROHIBITED?

It is unlawful for an employer, to fire you or discriminate against you with respect to pay, benefits, or working conditions because you help the NRC or raise a safety issue or otherwise engage in protected activities. Violations of Section 211 of the Energy Reorganization Act (ERA) of 1974 (42 U.S.C 5851) include actions such as harassment, blacklisting, and intimidation by employers of (i) employees who bring safety concerns directly to their employer or to the NRC; (ii) employees who have refused to engage in an unlawful practice, provided that the employee has identified the illegality to the employer; (iii) employees who have testified or are about to testify before Congress or in any Federal or State proceeding regarding any provision (or proposed provision) of the ERA or the Atomic Energy Act (AEA) of 1954; (iv) employees who have commenced or caused to be commenced a proceeding for the administration or enforcement of any requirement imposed under the ERA or AEA or who have, or are about to, testify, assist, or participate in such a proceeding.

HOW DO I FILE A DISCRIMINATION COMPLAINT?

If you believe that you have been discriminated against for bringing violations or safety concerns to the NRC or your employer, you may file a complaint with the NRC or the U.S. Department of Labor (DOL). If you desire a personal remedy, you must file a complaint with the DOL pursuant to Section 211 of the ERA. Your complaint to the DOL must describe in detail the basis for your belief that the employer discriminated against you on the basis of your protected activity, and it must be filed in writing either in person or by mail within 180 days of the discriminatory occurrence. Additional information is available at the DOL web site at www.osha.gov. Filing an allegation, complaint, or request for action with the NRC does not extend the requirement to file a complaint with the DOL. To do so, you may contact the Allegation Coordinator in the appropriate NRC Region, as listed below, who will provide you with the address and telephone number of the correct OSHA Regional office to receive your complaint. You may also check your local telephone directory under the U.S. Government listings for the address and telephone number of the appropriate OSHA Regional office.

WHAT CAN THE DEPARTMENT OF LABOR DO?

If your complaint involves a violation of Section 211 of the ERA by your employer, it is the DOL, NOT THE NRC, that provides the process for obtaining a personal remedy. The DOL will notify your employer that a complaint has been filed and will investigate your complaint.

If the DOL finds that your employer has unlawfully discriminated against you, it may order that you be reinstated, receive back pay, or be compensated for any injury suffered as a result of the discrimination and be paid attorney=s fees and costs.

Relief will not be awarded to employees who engage in deliberate violations of the Energy Reorganization Act or the Atomic Energy Act.

WHAT WILL THE NRC DO?

The NRC will evaluate each allegation of harassment, intimidation, or discrimination. Following this evaluation, an investigator from the NRC=s Office of Investigations may interview you and review available documentation. Based on the evaluation, and, if applicable, the interview, the NRC will assign a priority and a decision will be made whether to pursue the matter further through an investigation. The assigned priority is based on the specifics of the case and it=s significance relative to other ongoing investigations. The NRC may not pursue an investigation to the point that a conclusion can be made whether the harassment, intimidation, or discrimination actually occurred. Even if NRC decides not to pursue an investigation, if you have filed a complaint with the DOL, the NRC will monitor the results of the DOL investigation.

If the NRC or the DOL finds that unlawful discrimination has occurred, the NRC may issue a Notice of Violation to your employer, impose a fine, or suspend, modify, or revoke your employer=s NRC license.

To report safety concerns or violations of NRC requirements by your employer, telephone:
NRC SAFETY HOTLINE
1-800-695-7403

To report incidents involving fraud, waste, or abuse by an NRC employee or NRC contractor, telephone:
Office of the Inspector General Hotline
1-800-233-3497

REGIONAL OFFICE ADDRESS
U.S. Nuclear Regulatory Commission, Region II
Atlanta Federal Center
61 Forsyth Street, S.W.
Atlanta, GA 30303-3415
Telephone: 800-577-8510

Radiation Safety Manual: Radioisotopes

1.0  Program

Introduction

This manual describes the radiation safety program at Radford University for the use of radioisotopes. Information on the fundamentals of radiation, safety procedures, methods to reduce exposures, and State, Federal and University regulations concerning the safe use of radioactive materials are included.

Radioisotope work is regulated by the Nuclear Regulatory Commission and the State Bureau of Radiological Health. In order to work with radioisotopes, the NRC has issued a license to the university which contains a number of conditions that must be met. A copy of the license may be obtained from the Safety Office. This manual is based upon the Federal and State regulations and contains the specific rules that must be followed for use of radioactive material at the University. Individuals authorized to use radioisotopes must comply with all Federal, State, and university regulations and procedures in order to protect both the user and other personnel from unnecessary exposure to radiation.

Organization

Radiation Safety Committee

The Radford Radiation Safety Committee has been established by the University with the authority to regulate the safe use of radioisotopes, x-ray equipment, and non-ionizing radiation. The Radiation Safety Committee shall perform the following functions:

  1. Review and interpret Federal and State regulations, develop University regulations and oversee their implementation.
  2. Approve all applications for the use of radioisotopes and x-ray equipment and monitor the operation of the facilities and users.
  3. Approve "new experiments" which differ in size, kind, and/or scope from previous experiments.
  4. Review violations for failure to comply with regulations developed by the committee.

Members of the committee are appointed by the Chair of the Radiation Safety Committee. They are selected on the basis of their experience in the safe handling of radioactive materials, x-ray equipment, or non-ionizing radiation. An individual with administrative responsibilities shall chair the committee. The Radiation Safety Officer is an ex-officio member of the committee. At least one user of radioisotopes and one analytical x-ray user will serve on the committee. Additional members as deemed necessary may be approved by the Chair. Members will serve for three years and may be re-appointed upon completion of their terms. A member who misses three consecutive meetings without approval of the Chair will be considered to have resigned.

A meeting of the committee will be held at least quarterly. Additional meetings will be convened by the Chair as necessary. Minutes of the meetings shall be recorded and distributed to the members of the committee and other interested persons. A quorum shall consist of half the members plus one. The Chair and the Radiation Safety Officer have the authority to act on behalf of the committee for those occasions that do not warrant a special meeting of the full committee (e.g., approval of an amendment).

Decisions of the full committee are effective immediately. Decisions made at interim meetings are tentative, pending approval by the full committee. A member may request a review by the Radiation Safety Committee if a decision is not unanimous. The decision will not be implemented pending this review.

Radiation Safety Officer

The Radiation Safety Officer (RSO) will administer the radiation safety program at the university and advise others in the safe use of ionizing and non-ionizing radiation. The RSO will ensure that:

  1. Radiation safety activities are performed in accordance with approved procedures and regulatory requirements.
  2. Radiation surveys are performed.
  3. Quarterly reports of incidents, materials received, and an inventory of radioactive material and x-ray equipment are prepared for the Radiation Safety Committee.
  4. A current list of authorized users of radioisotopes and x-ray equipment is maintained, indicating any additions or deletions.
  5. Licensed materials are limited to the kinds and quantities listed on the license.
  6. Annual audits are performed to ensure that:

        NRC and DOT regulations and the terms of the license are followed.
        Occupational doses and doses to members of the public are ALARA.
        Required records are maintained.
  7. Radiation safety training and annual retraining for individuals using licensed materials are performed to include participation in a "dry run" of emergency procedures and a review of operating and emergency procedures, regulatory changes, and deficiencies identified during annual audits.
  8. Personnel monitoring devices are used as required and reports of personnel exposure are reviewed in a timely manner.
  9. Licensed material is properly secured against unauthorized removal at all times when not in use.
  10. Proper authorities are notified in case of accident, damage to licensed materials, fire, or theft.
  11. Results of audits, deficiencies, and recommendations for change are documented, provided to management for review, and prompt action is taken to correct deficiencies.
  12. Audit results and corrective actions are communicated to all personnel who use licensed material.
  13. All incidents, accidents, and personnel exposure to radiation in excess of ALARA or Part. 20 limits are investigated and reported to NRC and other authorities as appropriate, within required time limits.
  14. Licensed materials are disposed of properly.
  15. The license is amended when changes in licensed activities or responsible individuals occur.

Users of Radioactive Materials

Authorized User
- An authorized user may independently purchase, possess, and use radioisotopes. The authorized user is directly responsible for the laboratory and the users on the authorization. Authorized users must be approved by the Department Head.

Principal User - A principal user works under the indirect supervision of an authorized user and may supervise other workers and request amendments to the authorization. Principal users are typically professors appointed by the authorized user to supervise experiments.

General User - A general user works with radioisotopes under the indirect supervision of an authorized or principal user. General users have no supervisory authority and may not request amendments. General users may be professors, technicians, or students doing independent research.

Student User - Student users work with radioisotopes only as part. of a classroom requirement approved by the Radiation Safety Committee. Student users must be under the direct supervision of an authorized or principal user.

Responsibilities of Authorized Users

Authorized users are responsible for the safe use of radioisotopes under their control. Authorized users will ensure that:

  1. Users are adequately instructed in safety procedures and skilled in the safe use of radioisotopes.
  2. Users have received training in radiation safety principles as considered necessary by the Radiation Safety Committee.
  3. Written safety rules and procedures are provided to all users of radioisotopes.
  4. All users have been authorized to use radioisotopes by the Radiation Safety Committee.
  5. Equipment, facilities, and the use of radioisotopes meets all applicable federal, state, and local regulations.
  6. Users wear the appropriate personnel monitoring devices.
  7. The Radiation Safety Officer is notified of any changes in the equipment, facilities, or personnel using the equipment.

Responsibilities of Users

Individuals who use radioisotopes shall:

  1. Observe the radiation safety rules presented in this manual for the use of radioisotopes.
  2. Immediately notify the authorized user or the RSO of any deficiencies in radiation protection devices and procedures.
  3. Wear the appropriate personnel monitoring device.
  4. Know what to do in the event of a radiation emergency.
  5. Maintain radiation doses at a level that is low as reasonably achievable (ALARA).

Obtaining an Authorization

  1. An individual wishing to become an authorized user must submit an application form to the Radiation Safety Officer. The application will be submitted to the Radiation Safety Committee for review. The applicant will be notified within two weeks as to whether the application has been approved. A copy of the approved form will be sent to the applicant's department head.
  2. Before an application can be approved, the applicant must pass the radiation safety exam or be granted an exemption by the Radiation Safety Committee.

Radiation Safety Training

Users of radioisotopes must receive training and demonstrate competence in the following radiation safety principles:

  1. General properties of ionizing radiation.
  2. Survey equipment and personnel monitoring devices.
  3. Radiation hazards associated with the use of radioisotopes.
  4. Biological effects of ionizing radiation.
  5. Procedures to minimize exposure.
  6. Radiation safety regulations.
  7. Emergency procedures.
  8. Radford University’s radiation safety program.

Competence will usually be demonstrated by passing a written examination administered by the RSO. Exceptions to taking the examination may be granted by the Radiation Safety Committee because of previous training, experience, or education. Individuals wishing to seek an exemption should submit a request in writing to the RSO or the Chair of the Radiation Safety Committee.

Individuals who need training in radiation safety principles should call the Radiation Safety Officer at 831-5860 to obtain a copy of the Radioisotope Safety Manual. A test will be scheduled after the user has reviewed the training manual. A personnel monitoring device will be ordered, if necessary, after the individual has passed the test. Radioisotopes cannot be used until the monitoring device has been issued. An amendment to the authorization signed by the authorized or principal user must be submitted to the RSO prior to use of radioactive materials.

Request for Inspection

Any user who believes there has been a violation of the rules presented in this manual may request an inspection by notifying the Safety Office at Radford University or the Bureau of Radiological Health. The user's name will be kept anonymous. During the inspection, safety representatives may confer privately with users. Users may bring to the attention of safety representatives any past or present condition they believe may have contributed to or caused a violation. An authorized user shall not dismiss or discriminate against a user because a complaint was filed. The RSO will bring any complaints to the attention of the Radiation Safety Committee.

Variance

  1. An authorized user may apply to the Radiation Safety Committee for an exemption from these regulations. In addition to including the reason the variance is being sought, the application must include alternative methods that will be employed to ensure that the health and safety of personnel and the environment will not be compromised.
  2. The application for a variance shall be sent to the RSO or the Chair of the Radiation Safety Committee. The request will normally be acted upon at the next regular scheduled meeting of the Committee. A special meeting may be called by the Chair if deemed necessary. The authorized user may be present at the meeting to discuss his/her request for the variance.

Experiments

Users shall submit protocols to the Radiation Safety Officer before an experiment can be performed. The documentation for the experiment shall include the following information and can be initially approved by the RSO, subject to final approval by the Radiation Safety Committee:

  • The purpose of the experiment.
  • A description of the experiment.
  • An analysis of the possible radiation hazards produced by the experiment.
  • Safety devices and procedures that will reduce hazards.

Radiation Protection

Exposure Limits

1. Radiation workers using radioisotopes shall not receive a dose in one calendar quarter greater than the following limits:

  • Whole body: 1.25 rem
  • Lens of the eye: 3.75 rem
  • Skin of whole body: 12.5 rem
  • Extremities: 12.5 rem

2. Individuals under 18 years of age are not permitted to receive a dose greater than 10% of the above limits.

3. The maximum permissible whole-body dose to a pregnant radiation worker during the pregnancy shall not exceed 500 millirem.

4. Radiation levels to members of the public shall not exceed 2 mrem/hr or 100 mrem/yr.

ALARA Commitment

Although radiation doses from the use of radioactive materials are very low and current occupational limits provide a very low risk of injury, Radford University recognizes that it is prudent to avoid unnecessary exposure. It is therefore the policy of Radford University to reduce exposures to a level that is as low as reasonably achievable (ALARA). This will be accomplished through solid radiation protection planning and practice, as well as a commitment to policies that promote vigilance against unsafe practices.

Personnel Monitoring

  1. All personnel who enter an area where it is likely they will receive greater than 10% of the maximum occupational dose limit shall wear a personnel monitoring device.
  2. The need for a personnel monitoring device will be determined by the RSO. The RSO will order, distribute, and collect the monitoring devices.
  3. Whole-body personnel monitoring devices shall be worn routinely on the waist, shirt pocket, or collar. Thermoluminescent dosimeters (TLD's) and film badges shall not be worn in the pocket or obstructed in any manner. This badge must be worn on the outer clothing between the waist and neck. The position of the badge should remain the same during the entire three month period.
  4. When not in use, personnel monitoring devices shall be stored in an area where they will not be exposed to ionizing radiation above background levels.
  5. Badges are individually assigned and must be worn by one person.
  6. Personnel monitoring devices shall not be deliberately exposed to radiation except under the supervision of the RSO.
  7. Personnel monitoring devices are not to be worn during medical x-ray examinations. The badge is only for monitoring occupational exposure.
  8. Monitoring devices should be worn on the area of the body that is likely to receive the maximum dose.
  9. Pregnant radiation workers shall wear a whole-body monitoring device at the waist.
  10. A finger badge can be issued to monitor hand exposure. This badge should be worn on the hand expected to receive the highest exposure and worn with the label facing inward. Generally, a right handed person will receive more exposure to the left hand because more holding is done with the left hand. The ring badge should always be worn under gloves to avoid contamination.
  11. Badges are normally issued only to users of high energy beta and/or gamma emitting isotopes such as P-32, Cr-51, Hg-203 or Cs-137. Personnel that use H-3, C-14, S-35 or I-125 are not badged. Individuals that are issued badges must wear them anytime isotopes are received, handled or otherwise used.
  12. Any lost or damaged badges should be reported to the RSO promptly. A replacement will be acquired and a dose assignment will be determined. Normally badges will be exchanged by the RSO every 3 months (January, April, July and October). The old badges are sent to a commercial laboratory for determination of the radiation dose.

Exposure Records

Exposure records will be maintained by the RSO. The RSO will notify workers at least annually of their exposure to radiation. The RSO will supply the user with a written report if a dose in excess of 25% of the occupational limits is received. The RSO will provide a radiation exposure report to the worker, or an employer, at the request of the worker.

Pregnant Radiation Workers

Pregnant radiation workers shall wear a whole-body monitoring device at waist level and be informed of their radiation exposure on a quarterly basis. A pregnant radiation worker should notify the RSO as soon as her pregnancy is known, limit exposure to less than 500 mrem, and strive to reduce her exposure to the very lowest practical level.

Obtaining Radioactive Materials

  1. Only individuals authorized by the Radiation Safety Committee may order or receive non-exempt quantities of radioactive materials
  2. The request for radioactive materials must be signed by the Department Head. The order must include the name of the authorized user, isotope, activity, chemical form, and the supplier.
  3. All orders for radioactive materials must be approved by the RSO. The RSO will ensure that the requested materials and quantities are authorized by Radford's Radioactive Materials License.
  4. Requisitions without the approval of the Radiation Safety Officer will be returned to the originating department.
  5. During normal working hours all radioactive materials will be delivered to the Safety Office. After normal business hours radioactive materials will be delivered to the Police Department. Radioactive materials will be kept in a locked storage cabinet or room. Police Department personnel will be trained in proper procedures for handling packages. A package with obvious damage will not be accepted. The RSO or his assistant will deliver the package to the authorized user.
  6. Radioactive materials delivered to authorized users will be stored in an area approved by the RSO. Temporary storage areas will be secured to ensure that the materials are not removed by unauthorized personnel. Radiation levels in unrestricted areas will be kept ALARA and will not exceed the limits specified for members of the public.
  7. Transfer of radioactive material on campus from one laboratory to another must be approved by the Radiation Safety Officer. Transfer of radioactive material from the university to another university or company must be approved by the Safety Office. The RSO will send all packages from the University.

Record Keeping

1. The following records and documents will be maintained in the Safety Office:

  • NRC License and all amendments
  • Inventory records
  • Receipt, utilization, and disposal records
  • Transfer records
  • Personnel exposure records
  • Instrument calibration records
  • Leak test records
  • Incoming package survey records
  • Training records
  • Reports of unusual incidents
  • Additional records as specified by the license

2. Required laboratory survey records will be maintained in individual labs.

3. Authorized users must maintain a running log of each radioactive isotope in his/her possession, to include: receipt, usage, quantity on hand, and final disposition. All contamination surveillance records must also be maintained. The proper keeping of these records is very important to demonstrate appropriate use and disposal of all isotopes. In order to simplify record keeping, no decay corrections should be performed on these records.

2.0  Laboratories

Marking & Labeling

  1. Rooms, and areas, and where radioactive materials are used or stored shall be clearly marked with the proper warning labels. The standard label or sign contains the three-bladed radiation symbol and appropriate words with the colors of magenta on a yellow background. Equipment that may be contaminated must also be labeled. Some examples are: centrifuges, flasks and traps, filtering apparatus, pipetters, forceps, scissors, and tube racks.
  2. Each area or room where radioactive materials are used or stored (except natural uranium or thorium) in quantities greater than 10 times the quantities listed by NRC regulations (or 100 times the quantities listed if natural uranium and thorium are used), must be posted with the standard sign and the words: CAUTION RADIOACTIVE MATERIAL. Exceptions to this rule are in cases where:
    1. The radioactive material is a sealed source and the radiation level at 12 inches from the surface of the source container does not exceed 5 mR per hour.
    2. The radioactive material is used in a restricted area and:
          is in use for less than 8 hours, and;
          is constantly attended during the period by a person trained in radiation safety.
  3. A restricted area is any area where access is controlled by the university to protect individuals from exposure to radiation and radioactive materials.
  4. A Radiation Area is any area accessible to personnel where there exists radiation at such levels that a major portion of the body could receive either over 5 mR in any one hour or over 100 mR in any 5 consecutive days. Each such area must be clearly marked with a standard radiation sign bearing the words: CAUTION RADIATION AREA.
  5. A High Radiation Area is any area accessible to personnel where there exists radiation at such levels that a major portion of the body could receive over 100 mR in any one hour. Each such area must be clearly marked with a standard radiation sign with the words: CAUTION HIGH RADIATION AREA.
  6. An Airborne Radiation Area is any area that fits the following definition:
    1. Any room, enclosure, or operating area where airborne radioactive materials exist in concentrations above the amounts specified in NRC regulations Part 20; or
    2. Any room, enclosure, or operating area where airborne radioactive materials exist in concentrations that, averaged over the number of hours in any week when individuals are in the area, exceed 25% of the amounts specified in Part 20.
    3. Any such area shall be clearly labeled with a standard radiation sign with the words: CAUTION AIRBORNE RADIOACTIVITY AREA.
  7. Each container in which radioactive material is used, stored, or transported shall be labeled with: the radiation symbol, the words: CAUTION RADIOACTIVE MATERIAL, and the isotope, quantity, and date of measurement.
  8. Labeling is not required if either the quantity does not exceed NRC values or the containers are used intermittently in lab work with the user present.

Ventilation

  1. Adequate ventilation must be provided, equivalent to that needed for chemical operations. The university has established 6 air changes per hour as the standard in the absence of specific regulatory rules governing a given operation.

Storage

  1. All radioactive material under the control of a specific Authorized Principal User must be stored in a secure, lockable storage area. If more than one user shares a common facility, all radioactive material belonging to each user shall be segregated in such a way that no accidental transfer of material can occur.

Work Areas

  1. Work areas shall be defined within each laboratory. As much work with radioisotopes as possible must be done in the work area. If the radioactive material is used in a volatile form, or in such a way that aerosols could be readily dispersed, the work must be performed to minimize the airborne contamination.

Fume Hoods

As much work as possible should be done in a radioisotope-rated fume hood. Specifications for these hoods are as follows:

  1. The hoods should be designated as a Radioisotope Fume Hood by the vendor.
  2. The interior should by one-piece, seamless material, with coved corners free of joints, cracks or gaskets. The preferred material is stainless steel.
  3. Ducts must be stainless steel. Each hood must be ducted independently, directly to the roof.
  4. Blowers must be roof-mounted, spark-proof, explosion-proof units, sized by Facilities Management. Minimum flow must be 100 feet per minute (fpm) and maximum flow must be 150 fpm at permissible sash openings.
  5. A HEPA filter must be used in the exhaust duct if the unit is to be heavily used for radioisotope work.
  6. New units should have an air motion sensor and alarm to ensure proper air velocity and direction.
  7. It is recommended that the sash opening be minimized (less than 18 inches). Any equipment in the hood and work done in the hood should be as far from the opening as possible.
  8. Location of the hoods within a facility must be done in cooperation with Facilities Management and the Safety Office. Hoods shall be located as much as possible in a draft-free, low traffic area. It should not be necessary to pass a hood to escape from an area in case of fire, or an accident involving radioactive contamination, or some other emergency.
  9. When maintenance on a hood is required , a check for contamination must be performed before any work is done. The Safety Office must certify that the hood is working properly before it is returned to service.

Equipment & Work Surfaces

  1. Bench tops should be constructed of an impervious material such as stainless steel (unless P-32 is used) or stoneware. The integrity of these surfaces leads to easy decontamination. To avoid unnecessary decontamination activities, work areas should be covered with plastic backed absorbent paper.
  2. Installed vacuum lines should not be used for radioactive work unless no other alternative is present. If these lines must be used, traps and filters must be incorporated into the apparatus to protect the vacuum system. The ideal vacuum system would consist of a vacuum pump exhausting into a fume hood.
  3. The use of equipment solely for isotope work reduces the potential for spread of contamination and avoids the potential exposure of personnel not working with isotopes. Examples of such designated equipment are: microfuges, water baths, incubators, pipetters, electrophoresis equipment, and filtering apparatus.
  4. The majority of radioactivity is contained in the isotope stock vials. Adequate storage is critical to ensuring no contamination problems. The use of an enclosure for these stocks is an effective control, such as using Rubbermaid products. Storage areas should be lined with absorbent paper.
  5. One sink should be designated for decontamination activities. This area must be monitored frequently to insure no contamination.

Security

  1. Radioactive material must be protected from removal by unauthorized personnel. Visitors must be protected from exposure to radiation emitted from the radioisotopes used in the laboratory.
  2. The lab must be locked whenever an authorized user is not present. This precaution ensures that radioactive waste or radioactive experiments in progress are protected from unauthorized access.
  3. Storage areas of stock vials such as refrigerators must be locked when not in use or unattended by authorized personnel.

Inspections

  1. To ensure that radioisotopes are being used safely, all licensed activities are subject to inspection by the RSO. Inspections may be announced or unannounced and will be conducted at least every six months. A written report citing any deficiencies will be sent to the authorized user.
  2. The authorized user should correct the deficiencies within the time specified in the report unless a variance or an extension of time has been granted by the Radiation Safety Committee. An authorized user who disagrees with the deficiencies cited in the report may appeal in writing to the Radiation Safety Committee and request a hearing.

Surveys

Periodic surveys must be performed to show control of contamination. Additionally, the affected area must be surveyed any time a contamination incident is suspected. The recommended surveillance technique is to perform the daily checks with a portable survey instrument, while the weekly checks would be done with swipe tests analyzed in scintillation counters.

General

1. Keep a record of survey results. It must include the following information:

  • The date, area surveyed, and equipment used.
  • Name of person who made the survey.
  • A drawing of the area surveyed.
  • Measured dose rate or contamination level.
  • Actions taken if permissible limits are exceeded.

Packages

1. The following procedures will be used when opening packages containing licensed radioactive materials:

  • Always wear gloves when opening packages to prevent hand contamination.
  • Visually inspect the package for any signs of damage (e.g., wet or crushed).
  • Call the RSO if damage is noted.
  • Perform a leak test on the source or the final source container.
  • Assay the wipe sample to determine if there is any removable contamination.
  • Monitor the packing material and the empty package for contamination before discarding.
  • Remove any labels bearing the radiation symbol before discarding the package.

2. The RSO or his assistant will perform a wipe test on the exterior of the package and the source container. The exposure rate at 1 meter and at the package surface will be measured with a Geiger counter. Sealed sources will be leak tested. Results of package surveys will be maintained by the RSO.

3. The contamination limit for wipe tests on incoming packages is 220 DPM/100 sq cm. Exposure rates limits for packages with yellow II or III labels are 200 mr/hr at the surface or 10 mr/hr at 1 meter from the surface. The dose rate limit for packages with white I labels is 0.5 mr/hr at the package surface or 0.05 mr/hr at 3 feet.

Unsealed Sources

  1. The immediate work areas must be checked at least once daily (for labs using only H-3, weekly surveys are required). Weekly surveys must be performed to include the entire lab particularly eating areas, phones, door knobs, handles, etc. Record the dose rate in mR/hr and contamination levels in DPM/100 sq. cm.
  2. To determine the ambient dose rate, monitor the work area with a GM survey meter and pancake probe. Turn the meter to its most sensitive scale, select fast response, and monitor at a rate of approximately 1 inch per second. Keep the probe as close to the surface as possible without touching. If a reading above background is detected turn the meter to slow response and calculate the DPM as follows: gross CPM - background CPM = net CPM; net CPM/efficiency = DPM. The pancake GM probe may be used to detect alphas above 3.5 MeV, betas above 35 KeV, and gammas above 6 KeV.
  3. To survey for removable contamination, rub a piece of filter paper over a 100 sq. cm. (approx 16 sq. in.) area using moderate pressure. Count the filter paper in an instrument that is sufficiently sensitive to detect the presence of 220 DPM/sq. cm. A liquid scintillation counter should be used to count alpha emitters and low energy beta emitters such as carbon-14, and tritium.
  4. The maximum permissible limits of contamination for beta and gamma emitters are:
  • Unrestricted area- 220 DPM/100 sq cm loose, 0.05 mr/hr fixed
  • Restricted area- 1000 DPM/100 sq cm loose, 1.0 mR/hr fixed

Contamination from alpha emitters should be non-detectable. Contact the RSO if these limits are exceeded.

Sealed Source Leak Test Procedures

  1. Sealed sources containing more than 100 microcuries of a beta or gamma emitter, or 10 microcuries of an alpha emitter will be leak tested at six month intervals by the RSO.
  2. Prepare a separate wipe sample for each source. A cotton swab, filter paper, or tissue paper is acceptable. Moisten the swab slightly with water.
  3. Put on disposable gloves and wipe the entire accessible surface area of the source. For plated sources wipe only the inside of the container, do not wipe the surface of a plated source. Use tongs to wipe the sample if the surface dose is greater than 1 rem/minute.
  4. Place the wipe in a holder and record the activity and name of the isotope.
  5. An instrument that is sufficiently sensitive to detect 0.005 microcuries of activity will be selected. A thin window "pancake" GM probe with a window thickness of 1.7 mg/square centimeter will be used (Eberline E-120, HP 260 probe). The Geiger counter will be put on slow response and the probe placed as close to the wipe as possible. The Geiger counter is calibrated yearly by GP Instrument Services using a Cs-137 source.
  6. Withdraw the source from use and notify the Bureau of Radiological Health if the wipe sample activity is greater than 0.005 microcuries. To convert instrument CPM to microcuries use the following formulas:  
  • gross CPM - background CPM = net CPM
  • net CPM/efficiency = DPM
  • DPM/2.22 X E6 = microcuries

3.0  Handling Radioactive Materials

Efforts should also be made to keep internal radiation exposures ALARA. Radioactive material can be internally deposited if there is: skin contact, inhalation or ingestion. The use of good cleanliness practices coupled with adequate contamination surveillance can avoid skin contamination problems and the associated ingestion or skin absorption hazard. Airborne radioactivity can pose a significant inhalation problem. Procedures that generate aerosols or produce volatile or gaseous products should be performed in closed apparatus. For instance, capped tubes should be vortexed and closed systems should be used in conjunction with filters or traps when volatile or gaseous products are expected. If absolute containment is not achievable, the work must be performed in a fume hood.

Personnel Protective Equipment

  1. The use of protective equipment is always required when isotopes are used in an unsealed form. The extent of equipment is determined by the potential hazards. The minimum protection required is gloves. Double gloves would be advisable when higher levels of activity are used. Because various chemical forms are used, the choice of glove composition should be made according to chemical resistance.
  2. A laboratory coat is recommended to provide protection to exposed skin and personal clothing from spills.
  3. Eye protection is required in many situations; this includes safety glasses, goggles or a full face shield. Generally, the hazards associated with these requirements are: flying glass, liquid splashing or spattering, and fumes or particles. Contact lenses should not be worn during chemistry operations due to the risk of eye injury and the associated difficulty in removing the lenses.
  4. Respiratory protection may be necessary when the generation of fumes, mists or particles cannot be controlled by an enclosure. A dust mask can be used for protection from particulates in the air. Exposure to fumes, mists and fine particulates can only be controlled by wearing a half-face respirator. The respirator must be equipped with filters capable of removing the specific hazard. Respirators are issued to individuals by the Safety Office. Prior to issuance the individual must be medically evaluated by a physician to ensure that the person is physically capable of using a respirator.

Unsealed Sources

  1. Wear a lab coat or other protective clothing whenever the possibility of contamination exists. Do not wear potentially contaminated lab coats outside of the laboratory.
  2. Wear disposable gloves and eye protection when handling radioactive materials. Change gloves frequently if contaminated items are being handled.
  3. Always wash and monitor your hands before leaving the laboratory.
  4. Do not eat, drink, smoke, or apply cosmetics or store these items in any area where radioactive materials are used or stored.
  5. Never pipet by mouth.
  6. Whenever possible, use remote handling devices such as tongs or forceps when working with significant activities of gamma emitters or high energy beta emitters. Work should be performed behind protective shields such as lead and/or Plexiglass. Do not work over open containers of beta emitters. Keep strong gamma and beta emitters in shielded containers. Always use radioactive materials in a manner that will ensure that radiation exposure rates are kept as low as possible.
  7. Use disposable absorbent paper or lipped trays to protect work surfaces and to confine spills. The tray should be large enough to contain any spill. Perform work in a fume hood if a potential for airborne contamination exists.
  8. Do not leave radioactive materials in uncovered containers. Label all containers that will be stored over night and store so that the dose rate at the surface of the storage area does not exceed 2 mR/hr.
  9. Wear required personnel monitoring devices at all times when working with radioactive materials. The need for monitoring badges will be determined by the RSO.
  10. Dispose of radioactive waste only in designated, labeled, and properly shielded containers. The RSO will be responsible for the ultimate disposition of radioactive waste.
  11. Perform routine radiation surveys of areas where radioactive materials are used or stored to ensure that contamination and radioactive dose levels are below permissible limits. If necessary decontaminate or secure the area.
  12. Routinely monitor hands, feet, and clothing for radioactive contamination before leaving the laboratory.
  13. Conduct a "dry" run without radioactive materials when working with new procedures and new personnel to determine potential problem areas.
  14. Know where spill materials are kept and be familiar with the procedure for decontaminating a small spill.
  15. Transport radioactive materials in a "double container" to confine possible spills. Provide adequate shielding to ensure that permissible levels in unrestricted areas are not exceeded.
  16. Store radioactive materials in a secure and protected area that will prevent unauthorized use. Ensure that radiation levels in unrestricted areas are not exceeded. Immediately report the loss or theft of radioactive materials to the RSO.
  17. Post radioactive work areas, laboratories, and containers of radioactive materials with the appropriate warning signs.
  18. Keep contaminated glassware and equipment separate from uncontaminated utensils. Maintain high levels of cleanliness and good housekeeping at all times.
  19. Report all injuries possibly involving radioactive materials to the RSO to determine if the wound is contaminated.

Sealed Sources

  1. Use sealed sources under the supervision and immediate control of an individual authorized by the Radiation Safety Committee.
  2. Do not eat, drink, or smoke in areas where sources are used or stored.
  3. Areas where radioactive sources are used and stored will be approved by the Radiation Safety Committee.
  4. Handle sources in designated areas of the laboratory.
  5. Store sources in a box marked with a radioactive materials label. When not in use lock the room or keep the sources in a locked cabinet or drawer.
  6. Do not handle radioactive sources with bare hands. Use protective gloves, forceps, or containers to handle sources.
  7. Keep the length of time that sources are used to a minimum, maximize distance from sources, and provide shielding where practical to reduce radiation levels to ALARA levels.
  8. Persons handling exempt quantities will receive a short training course in basic radiation safety principles and safe handling procedures. Users will sign a training acknowledgment form. Training may be performed by the Authorized User or the RSO. Training is not required for individuals watching demonstrations.
  9. Individuals handling non-exempt quantities of radioactive materials will be trained as radiation workers. Users will complete a full radiation safety course and pass a test administered by the RSO.
  10. Immediately report the loss, theft, or release of non-exempt quantities of radioactive materials to the RSO.
  11. Post laboratories using or storing non-exempt radioactive sources with a Radioactive Materials sign, Notice to Employees, and Emergency Procedures Notification. Post Radiation Area signs if it is possible to receive a dose greater than 5 mr/hr to the whole body.
  12. Do not exceed exposure levels in unrestricted areas of 2 mr/hr.
  13. Check non-exempt sealed sources in use for leakage every 6 months. Withdraw the source from use if the wipe sample activity is greater than 0.005 uCi.
  14. Inventory sealed sources every 6 months. Perform a radiation survey of storage areas every 3 months.
  15. Radiation sources, their containers, or a tag will bear the radiation symbol, the words "Caution Radioactive Material", isotope name, activity, and date of calibration. Radiation levels will be included if greater than 5 mr/hr at one foot.
  16. A calibrated survey instrument capable of detecting the radiation in question must be available to monitor areas in which non-exempt sources are used. Conduct a survey weekly to ensure that sources have been returned to their shielded containers or areas.

Phosphorus-32

  1. Glasses, safety glasses or goggles must be worn to provide adequate eye protection from the beta particles of P-32. A lab coat should be worn to protect against skin and personal clothing contamination. Gloves must always be worn when handling any material. Two pairs of gloves should be worn when dispensing from stock solutions.
  2. A survey instrument must be on during use so hands can be checked periodically. After use of P-32, the lab coat and hands should be surveyed carefully. If the lab coat is contaminated survey yourself under the lab coat. All areas and equipment used should also be surveyed, particularly microcentrifuges.
  3. In order to determine personnel radiation exposures, body and ring badges are to be worn. Since the ring badge should be recording the maximal hand exposure, the TLD chip should be turned toward the inside of the hand.
  4. Any time new procedures or techniques are used, dry runs without radioactivity should be performed. Particular attention must be paid to the production of aerosols or steps where unshielded body or hand exposures are possible. Unshielded exposures should be avoided.
  5. Vortexing and sonicating samples can cause aerosol production. These operations should be done in a hood and the tubes covered with parafilm or aluminum foil. After the agitation is complete, the cover should not be removed for approximately one minute to allow the aerosol to settle.
  6. Adequate shielding should be available when P-32 is used. The following are the minimum thickness required: 0.33 inches of water, 0.25 inches of plexiglass, 0.19 inches of glass, and 0.13 inches of aluminum. Use of denser materials for shielding can cause considerable bremsstrahlung production. Glass shielding should be minimized when greater than 5 mCi are used at one time because considerable bremsstrahlung cab be produced.
  7. For bench top work a plexiglass stand with an angled top piece offers excellent body shielding. Work should be done behind this plexiglass shield on a tray lined with absorbent material.
  8. A section of PVC pipe with a slightly larger inner diameter than the waste jugs is an inexpensive and effective shield for liquid waste as long as a plexiglass cover is used on the pipe. It is preferable to use heavy duty plastic jugs for liquid waste.
  9. Two thickness of tygon tubing make an excellent beta shield for handling eppendorf tubes or test tubes. Use of a "Hot Hand" hand protector (Lab Safety Supply) or equivalent will shield the hand adequately when picking up tubes or other containers. Aluminum tongs can be used for remote handling. If tygon tubing is put on its ends, these tongs grip very effectively. Blocks of aluminum or plexiglass with holes for tubes make excellent shields during incubation or as routine holding racks.

Airborne Radioactivity

  1. Radioactive contamination of areas or equipment pose a potential hazard to the inside of the body. This may take place by skin absorption or ingestion. If radioactive contaminants become airborne, an inhalation potential can be created throughout the lab. The airborne problem can be caused by aerosol production, volatility of products or radioactive gases.
  2. There are a number of situations that may cause aerosol production. The use of a vortex unit to mix tubes or containers may cause an aerosol to be produced. Aerosols can be avoided by capping or applying parafilm to the tops of tubes. After agitation the tube should not be opened for about a minute to allow the aerosol to settle. A sonication device will also create an aerosol. This operation must be performed in a fume hood while covered with parafilm or aluminum foil. Totally enclosed sonicator probes can be purchased and should be used whenever possible.
  3. The contamination of the inside tip of an eppendorf pipetter illustrates the ease for aerosol production. The simple actions of withdrawing and dispensing radioactive liquids cause the inside of the pipetter to become contaminated because of the aerosol generated. This cannot be avoided, but can be minimized by frequent contamination checks and decontamination. Pipetters must never be laid on their sides while liquid is in the tip.
  4. Centrifugation may inadvertently cause aerosol production. Generally, the use of screw cap tubes are preferred over snap top tubes. If any residual liquid is on the lip of the tube, this liquid will be deposited in the centrifuge once it begins to spin. Since the rotor moves very rapidly, a considerable amount of air passes through and out the bottom. This air can carry contamination. Another potential problem to be aware of is tube rupture. It is very important to use only tubes sized properly for the centrifuge and rated to withstand the centrifugal forces that will be encountered.
  5. Airborne problems can also be caused by using volatile compounds or generating volatile products. Volatile products can often be controlled by working within a charcoal filtered enclosure located inside of a fume hood.
  6. The use of radioactive gases or the generation of radioactive gases can cause airborne problems as well. Generally, these types of experiments should be performed inside of a fume hood. The radioactivity discharged to the environment must be calculated and compared to federal release limits in order to ensure compliance.
  7. One final airborne potential can exist when fine radioactive powders are used. Powders must be used in a draft-free area to avoid dispersion because of air movement. The ideal technique would involve the addition of an appropriate liquid through the serum stopper with a syringe to produce a stock solution. Otherwise, extreme care must be taken when the powder is weighed such as keeping the weighing pan covered.

Decontamination

Radioactive contamination must be corrected in a timely fashion. Exceptions to this are: pipetters, work trays, absorbent paper covered surfaces, or other equipment that is clearly marked with the caution symbol. Any contamination that is not confined to protected surfaces must be cleaned immediately.

Equipment

  1. Once equipment has been used with radioactive material, no alternate uses are allowed until it is shown to be clean. The equipment cannot be serviced in the lab, sent back to manufacturers or repair shops, or sent as surplus until proven to be clean.
  2. A number of decontamination techniques can be used to clean equipment. The two basic types of decontamination methods are corrosive and noncorrosive. Corrosive techniques are less desirable because surface material is often removed. This results in a surface that is harder to decontaminate in the future. The size of equipment, extent and chemical form of contamination and construction of equipment can dictate the technique used.
  3. If short half-life isotopes are used, storage of contaminated equipment for 7-10 half lives can be an effective decontaminant especially when radiation levels pose a hazard.
  4. Washing equipment with a special decontaminating solution (e.g. Radiacwash, Count-off, Lift-away) is recommended. Soaking for several hours in this solution can often remove more stubborn contamination. After the equipment has been cleaned, it must be dried before a final survey can be performed. The use of sprays such as Fantastik or Windex may be an effective decontaminant.
  5. Organic solvents such as ethanol or acetone could be used by wiping the equipment. This operation should be done in a fume hood. Acetone will react with plastic and should be avoided. Harsher methods involve soaking in dilute acids or bases. One additional method uses abrasives such as steel wool or sandpaper. Abrasives usually remove the surface layer which will increase the difficulty of future decontamination efforts.
  6. When the equipment cannot be cleaned below the limits, disposal as radioactive waste is necessary.

Areas

  1. Any areas such as bench tops or floors that become contaminated must be cleaned up promptly. Initially, a detailed survey must be performed to determine the extent of contamination. The affected area should be outlined with a wax pencil or magic marker. For very small areas with dry contamination, masking tape pressed on the area and removed may decontaminate effectively. For larger areas cleanup is best accomplished by applying a decontaminant solution to the area and working from low activity areas to high activity areas. If scrubbing with towels or sponges aren't sufficient, a brush should be used.
  2. Other methods involve organic solvents, acids, bases, and abrasives in a similar fashion to equipment cleaning. These steps must be performed under RSO supervision only. Widespread contamination or high activities must be cleaned under RSO supervision. Area contamination must be cleaned to below the limits. Removal of surfaces such as floor tile may be necessary if contamination cannot be cleaned adequately.

Radioactive Waste

  1. Carefully plan work with radioactive materials to minimize the volume of waste generated. Use care to separate radioactive from non-radioactive waste as it is generated. Do not place non-radioactive waste in radioactive waste containers. Segregate waste into appropriate categories; it is important that different types of waste not be mixed. Remove or deface all radioactive waste labels from packages before disposal.
  2. Authorized Users are responsible for ensuring that their waste is packaged, labeled, and recorded properly. Waste cannot be accepted by the RSO unless it has been correctly identified and tagged with a radioactive waste label.
  3. Radioactive waste will be disposed of by one of the following methods: release to the sanitary sewer in conformance with local and NRC regulations, decay in storage, or transfer to a licensed disposal site. The RSO will decide the most appropriate manner of disposal.
  4. Store radioactive waste only in restricted areas where it can be secured against unauthorized removal. Do not allow radioactive waste to accumulate in a lab. When a waste container is full, notify the RSO for removal to the central storage area.
  5. Place containers that may break in a secondary container that is large enough to hold the contents. Liquid containers must have a screw type lid.
  6. Separate radioactive waste into dry solids, aqueous, and non-aqueous waste. Dry solid waste is primary composed of paper, plastic, syringes, and glass that becomes contaminated during work with isotopes. No free liquid, other than trace amounts, is allowed in this type of waste. Liquid scintillation fluids constitute the major portion of non-aqueous waste.
  7. Collect dry solids in plastic-lined (thick walled) 5-gallon, 20-gallon, or 55 gallon containers. Waste containers must be approved by the RSO. Place syringes in smaller containers that are puncture resistant and tape the lid shut. Do not over fill the bag. Leave sufficient room at the top so the bag can be twisted and sealed with strong tape.
  8. Separate aqueous from non-aqueous waste. Collect bulk liquids in 1-gallon or 5-gallon plastic or glass containers. Do not use plastic milk jugs. Segregate aqueous liquids containing H-3 or C-14 from all other aqueous liquids to simplify sink disposal by the RSO.
  9. Collect all original solutions and first rinses as waste. Other rinses or equipment decontamination water can be released into the sanitary system if certain criteria are met. The liquid must be readily soluble or dispersible in water. The maximum release cannot exceed 1 uCi per day. Any release must be flushed with copious amounts of water.
  10. Pack scintillation vials in a separate labeled waste can lined with a thick plastic bag. Place a layer of absorbent material in the bottom. Collect the vials in an upright position. Segregate vials with specific activities less than 0.05 uCi/ml. In addition, Separate vials containing H-3 and C-14 with less than 0.05 uCi/ml from other vials.
  11. Segregate radioactive waste into the following categories based on half-life:

        Very short (less than 15 days) ex: P-32
        Short (15-65 days) ex: P-33, I-125
        Intermediate (65-90 days) ex: S-35
        Long (gtr than 90 days) ex: C-14, H-3

  12. Waste with half-lives less than 90 days will be stored at the university in the hazardous waste storage lockers. After 10 half-lives the waste will be surveyed and discarded in the regular trash if found to be at background levels. Waste with half-lives greater than 90 days will be shipped off site for disposal by and undetermined licensed firm.
  13. Prior to removal from the laboratory determine the activity of each isotope in the container as accurately as possible.
  14. The RSO will perform a contamination check of waste containers before they are removed from the laboratory. If a wipe of the outer surface shows contamination levels greater than 220 DPM the container will be decontaminated. Wipe tests will be recorded and maintained by the RSO.

Major Spills

Initial Response and Notification

1. Major spills are an immediate health hazard, spread over a large area, and contain removable activity greater than 10,000 disintegrations per minute (dpm).

2. Evacuate all personnel from the area. If possible, quickly surround the spill with absorbent booms to prevent the spread of contamination. Leave behind clothing and shoes that may be contaminated. Close doors and windows and lock or otherwise secure the area. If the spill involves airborne contaminants turn off the ventilation system in the area.

3. Do not allow unauthorized people into the room. Keep potentially contaminated people in a protected area. Do not attempt to decontaminate the spill.

4. Report the spill to the Police Department. Provide the following information and wait in a safe place for emergency personnel to arrive and direct them to the spill:

    Name and telephone number of the caller.
    Location of the spill.
    Name and quantity of materials involved.
    Extent of injuries, if any.
    Environmental concerns, such as the location of storm drains.
    Any unusual features such as foaming, odor, fire, etc.

5. The Police Department will call the Radiation Safety Officer, Vice President for Business Affairs, Assistant Vice President for Facilities, Assistant Vice President for Communications, and other appropriate university officials. The Vice President for Business Affairs will notify the President.

6. A Police Officer will proceed to the site and cautiously evaluate the situation while waiting for the Radiation Safety Officer. If there is clear danger to the occupants of the building the officer will evacuate the building.

7. The RSO will determine the severity of the spill and notify the Bureau of Radiological Health and the Nuclear Regulatory Commission if necessary. Decontamination will be conducted under the supervision of the senior emergency authority at the scene.

Minor Spills

Initial Response & Notification

  1. Minor spills do not constitute an immediate health hazard, are localized, and contain removable activity less than 10,000 dpm.
  2. Notify persons in the immediate area that a spill has occurred.
  3. Keep individuals that may be contaminated from leaving the area until surveyed. Delineate the contaminated area, restrict access and notify the Authorized User and the Radiation Safety Officer.

Specific emergency procedures

  1. Obtain the proper survey equipment and clean-up materials and decontaminate the area. Only properly trained individuals are allowed to clean up radioactive materials.
  2. Using disposable gloves and protective clothing, if necessary, prevent the spread of contamination by covering the spill with absorbent paper. Use wet paper to cover a dry powder spill.
  3. Clean up the spill, carefully folding the absorbent paper with the clean side out and place in a plastic bag. Wash the area with water, detergent, or a commercial "Radwash" cleaner. Use a minimum amount of water. Work from the outermost edges towards the center of the spill. Wipe up the water with absorbent paper. Place contaminated paper, gloves, and booties in a plastic bag for proper disposal. Survey the area with an appropriate survey meter and take wipe samples. Continue decontamination until the wipe sample is less than 1000 dpm/100 square cm and the fixed contamination is below 1.0 mR/hr.
  4. Decontaminate personnel by removing contaminated clothing and flushing contaminated skin with lukewarm water (not hot) and washing with mild soap. If necessary gently scrub the area with a soft bristled brush. Do not overly scrub the affected area. If necessary use a mild abrasive such as lava soap, or a 50:50 paste of cornmeal and detergent. Repeat 3-4 times, monitoring the skin between washes. Wipe samples taken on the skin should be non-detectable and fixed radiation levels should be below 0.05 mR/hr.
  5. Check the area around the spill, your hands, clothing, and shoes for contamination.

Fires

  1. If a fire involves radioactive materials immediately evacuate the area and call the Fire Department and the Radford University Police Department.
  2. The Police Department will call the Radiation Safety Officer, Vice President for Business Affairs, Assistant Vice President for Facilities, Assistant Vice President for Communications, and other appropriate university officials. The Vice President for Business Affairs will notify the President, if appropriate.
  3. If the fire does not immediately involve radioactive materials attempt to put out a small fire, or remove radioactive materials to a safer location.
  4. If non-exempt quantities of radioactive materials are involved, the RSO will immediately report the incident to the Bureau of Radiological Health.
  5. The Chief of the Fire Department or his designate will be the initial senior emergency response official at the scene.
  6. The Fire Department in cooperation with the RSO, and the Bureau of Radiological Health will assess the potential severity of the fire and request assistance from the Emergency Radiological Assistance Team, if necessary.
  7. The Radford University Police Department and the City Police Department will provide site security and crowd control.
  8. As other emergency response teams arrive the most senior emergency response official at the site will be in charge. All emergency responders and operations will be coordinated through this individual.

Loss of Radioactive Material

  1. Report any theft or loss of radioactive material to the Authorized User and the Radiation Safety Officer.
  2. The RSO will immediately report to the Bureau of Radiological Health by phone and confirm by letter any theft or loss of non-exempt quantities of radioactive materials

4.0  Fundamentals of Radioactivity
 
Atomic Structure

An atom is the smallest division of matter that still displays the chemical properties of an element. Atoms are composed of a dense positively charged nucleus containing neutrons and protons. The nucleus is surrounded by a cloud of negatively charged electrons. In neutral atoms the positive and negative charges are equal. The proton has a mass of approximately 1 atomic mass units (AMU) and a single positive unit of charge. The number of protons is known as the atomic number (Z) and defines the particular element. The neutron has a mass slightly greater than 1 AMU and has no charge. The number of protons and neutrons is called the mass number, represented by the symbol A. The electrons circle the nucleus in distinct orbits, called energy shells. These shells are labeled alphabetically, starting with the letter K, and going outward to the letter Q. An electrons mass is approximately 1\1840 that of a proton or neutron.

Atoms characterized by a particular atomic number and mass number are called nuclides. Nuclides with the same number of protons but different numbers of neutrons in the nucleus are called isotopes of that element. Isotopes of the same element have essentially the same chemical properties. For example, there are three isotopes of hydrogen. The simplest nucleus is ordinary hydrogen and consists of a single proton. Adding a neutron to the nucleus forms an isotope called deuterium. Adding another neutron produce an isotope called tritium. Tritium has an atomic number (Z) of 1 and a mass number (A) of 3. Symbolically this is written as H-3. The letter H describes the element as hydrogen with an atomic number of 1. The 3 stands for the mass number. The number of neutrons (2) is found by subtracting the atomic number from the mass number.

In addition to varying the number of neutrons and protons the number of electrons in an atom can change. An atom having the same number of protons and electrons is electrically neutral. Atoms with an unequal number of protons and electrons are called ions. A negative ion has more electrons than proton and a positive ion has a deficiency of electrons.

Radioactive Decay

The stability of an atom depends on the particular combination of neutrons and protons in the nucleus. An unstable atom has a nuclear energy imbalance due to an improper combination of neutrons and protons. To achieve stability the nucleus emits this excess energy in the form of high energy particles or gamma rays. The emission is termed radiation and the atom is called radioactive. For example, the two lightest isotopes of hydrogen are stable, while the third is unstable or radioactive. This means that tritium can spontaneously decay releasing radiation and change into another isotope. When this happens a negative electron, called a beta particle is emitted and one of the two neutrons becomes a proton. Thus an unstable isotope has decayed into a stable one, an isotope of helium. The beta particle is similar to ordinary electrons, except that it has kinetic energy to ensure conservation of energy.

Stable isotopes with light nuclei tend to have equal numbers of neutrons and protons. As the number of neutrons and protons increase, however, isotopes begin to have more neutrons than protons. This is because the protons are confined in a very small space and strongly repel each other due to their like charges. Since neutrons have no charge, more of them can be close together. However, nuclear forces prevent too many from being in a stable nucleus. The largest stable nucleus that has equal numbers of protons and neutrons is an isotope of calcium with 20 of each.

There can be both stable and unstable isotopes for a given element. Tin has the most stable isotopes, 10, while there are no completely stable isotopes for elements with atomic numbers greater than 83. Unstable isotopes decay until the decay product is stable. This may take more than one step. For example, in a chain decay one unstable isotope will decay to another unstable one, which will then decay to a stable one. There are several different ways in which an unstable isotope can decay.

Types of Radioactive Decay

Alpha Particles

Alpha decay occurs when a nucleus emits an energetic helium nucleus consisting of 2 protons and 2 neutrons. The alpha particle has a mass of approximately 4 AMU and a positive charge of 2 units. Alphas are emitted with discreet energies (monoenergetic), and typically have energies of 4 to 9 million electron volts (MeV). These particles are very heavy and have little penetrating power. A single sheet of paper, a few inches of air, or the top layer of skin will stop an alpha particle. Alphas are not considered an external hazard, however they are very hazardous if ingested. Alpha particles are relatively slow and create numerous ionizations along a short path. Alpha decay typically occurs in heavy nuclides such as uranium, radium, americium, and plutonium.

Beta Particles

Beta decay occurs when a nucleus emits a high speed negatively charged electron. The beta particle results from the energy released from the transformation of a neutron into a proton. Their maximum energies range from 0.015 to 3 MeV. Beta particles are not monoenergetic, but are emitted with an energy that can vary up to a maximum value for a given isotope. However only a small percentage of beta particles are released near the maximum energy. The average energy of release is approximately one-third the maximum energy. The range of beta particles in air is dependent on the maximum energy and can vary from 6 mm for H-3 to 6 m for P-32. In general the range of a beta particle in centimeters is approximately equal to the energy in MeV divided by two. Betas are more penetrating than alphas and can be stopped by several sheets of aluminum foil, one inch of wood or one-quarter inch of plastic. Beta emitters include H-3, C-14, P-32, S-35, Cl-36, and Ca-45.

Neutrons

Neutrons are particles with no electrical charge. Neutrons that are loosely bound in the nucleus can be dislodged by alpha particles. For example in a plutonium-beryllium (PuBe) source, neutrons are released when alpha particle from plutonium bombard the beryllium. Neutrons are also released in some heavy elements by nuclear fission processes. Fission may occur spontaneously in some nuclides, for example Californium-252, but the major source of neutrons is nuclear-fission reactors.

Gamma Rays

Gamma rays are very short wave electromagnetic radiations emitted by transformations in the nucleus. They are released as packets of energy called photons, travel at the speed of light, have no mass or charge, and are very penetrating. The release of gammas changes the energy state of the nucleus but does not change its structure. Gamma rays are released at discrete energies (monoenergetic) ranging from a few thousand electron volts (eV), up to approximately 3 MeV. Gamma rays lose their energy by collisions with orbital electrons. This results in the ejection of electrons and the creation of ions. Isotopes that decay by this process include Cr-51 Co-57, Co-60, Cd-109, I-125, and I-131.

Electron Capture

Electron capture occurs when the nucleus captures an orbital electron. A vacancy is left in the innermost orbital shell that is filled by an electron falling from a higher orbit. The excess energy is released as an x-ray photon. I-125 decays in this manner.

Positron Decay

A positron is an electron with a positive charge, the antiparticle to the negative electron. The positron eventually combines with a negative electron, annihilating both particles and creating two 0.51 MeV photons. Sodium-22 and fluorine-18 are example of positron emitters.

Half-Life

The half-life of a radioactive material is the time required for the initial activity of the substance to decrease by one-half. The half-life for a particular isotope is a constant and cannot be increased or decreased by any chemical or physical means. Half-lives range from microseconds to billions of years. Each radioisotope has its own unique decay rate. For example P-32 has a half-life of 14 days. This means that one-half will be gone in 14 days and one-half of the remainder will have decayed in another 14 days. After 7 half-lives less than 1% of the original activity will remain.

A common rule of thumb is that after 10 half-lives have elapsed, all activity is effectively gone. Since the activity decreases by a factor of 2 as each half-life passes, the activity after 10 half-lives will diminish by a factor of 1024, or to less than 0.1%. However, if there was originally a large amount of activity, there may still be considerable activity remaining even after 10 half-lives. For example, if there were originally 1 Curie of an isotope there would still be approximately 1 mCi remaining after 10 half-lives.

Activity

Radioactive decay occurs when the nucleus releases excess energy in the form of high speed particles or gamma rays. The number of transformations occurring per unit of time is called activity. A unit termed the Curie is used to describe the amount of activity in a radioactive material. The Curie is defined as 3.7 x 10 10 disintegrations per second (dps) or 2.22 x 10 12 dis/min. It refers to a fairly large amount of activity. In most cases the amounts of activity used in an experiment would be in the range of a few microcuries to a few millicuries. A useful quantity that is often used in laboratories is the amount of activity in a microcurie, 2.22 x 10 6 dis/min.

Activity refers to the number of nuclear disintegrations occurring per unit of time and is not necessarily equal to the number of particles emitted. The rate of emission is equal to the activity only when one particle is given off per disintegration. Numerous particles per disintegration may be given off and careful attention must be paid to the decay scheme. For example, the decay of 1 microcurie of Bi-212 produces 2.22 x 10 6 disintegrations per minute. This translates to an emission rate per minute of: (2.22 x 10 6) 0.36 for alpha particles, (2.22 x 10 6) 0.64 for beta particles, and (2.22 x 10 6) 0.36 for gamma rays. Gamma rays are associated with 72% of the alpha particles and 16% of the beta particles.

A new unit for activity that is part of the International System (SI) of measurements is called the Becquerel. Under this system 1 becquerel (Bq) is equal to 1 disintegration per second. One Curie is equal to 3.7 x 10 10 Bq. Although the Becquerel is widely used in Europe and the scientific community acceptance in the United States has been slow.

Specific Activity

Activity does not take into account the volume or mass of the radioactive material in which the decay process occurs. The term that describes the concentration of activity is specific activity (SpA). SpA is the number of curies or becquerel per unit mass or volume and is often expressed in units of Ci/g, mCi/ml, mCi/mm, etc. For example, if the activity of a radioactive material was 1 mCi and it had a SpA of 10 mCi/ml then the total volume would be 0.1 ml.
 
Interactions of Radiation with Matter

The two different kinds of radiation are particulate (alphas, betas and neutrons) and electromagnetic radiation (gamma rays, x-rays and bremsstrahlung). Each type of radiation interacts with matter in a unique way.

Charged particles have an electric field, similar to the orbital electrons of an atom. As a charged particle passes an atom the influence of its electric field can either remove an electron from the atom or raise an electron to an excited orbital state. The first process creates an ion pair while the second leaves the atom intact. Both types require energy which is derived from the kinetic energy of the incident particle. The kinetic energy of the particle is reduced by the amount of energy transferred during the interaction. These interactions continue until the particle loses all of its energy.

Alpha Particles

An alpha particle is a relatively large subatomic particle (4 AMU) that has a charge of +2. This causes the ionizations per unit length (linear energy transfer) to be high and the range of the particle to be very short. An alpha loses about 35 electron volts (eV) for each ion pair it creates in air or soft tissue. A typical alpha creates more than 100,000 ion pairs before all its energy is lost. Because these particles are monoenergetic, they have well defined ranges in matter. To illustrate its penetrability, a 4 MeV alpha has a range of approximately 2.3 cm in air and 0.003 cm in tissue. This is much less than the thickness of human skin which is approximately 0.1 cm. The greatest hazard posed by alpha radiation is from ingestion or inhalation, which allows the radionuclide to be deposited in tissue.

Beta Particles

Beta particles are also charged particles that interact with matter in basically the same way as alpha particles. Due primarily to the much smaller mass of the beta (1/1840 AMU), there are some differences. For a given energy, their speeds are much greater and they spend less time in the vicinity of an atom. This results in less interactions per unit distance. Since they have the same mass as orbital electrons, a large portion of their energy is given up to a target electron. Betas also lose energy by bremsstrahlung as their paths are bent by the electric fields of the nucleus and orbital electrons.

The absorption of betas also differs from alpha particles because they are not monoenergetic. Betas are emitted with energies ranging between 0 and a maximum value. The beta energies vary because a neutrino is emitted along with the beta and the maximum energy is shared between them. The interaction between the uncharged neutrino and matter does not transmit appreciable energy to any material it passes through.

Although a beta will penetrate much more deeply in matter than an alpha, the range is still not great. For example, the 1.71 MeV beta of P-32 has a range of about 0.8 cm in tissue (1/3 inch). In air the P-32 beta has a much greater range of 610 cm (20 feet). The advantage of using low energy beta emitters can be illustrated by comparing C-14 and P-32. The C-14 0.156 MeV beta has a range in tissue of 0.04 cm (1/25 inch) and a range in air of 31 cm (1 foot). Shielding is not necessary for C-14 while considerable shielding is necessary for P-32.

Bremsstrahlung is another energy loss mechanism for betas in which the beta energy is converted into x-rays. This occurs when the attractive forces from an atom cause the beta to rapidly decelerate and change its path. The quantity of bremsstrahlung increases as the shield density increases. The x-ray energies are determined by the incident beta energy, but their average energy is 1/3 of the maximum beta energy. The use of low atomic number shields (e.g. plastic) minimizes the production of bremsstrahlung.

Neutrons

Since neutrons are not charged, they interact differently with matter than charged particles. They can be scattered, absorbed by the nucleus of the target atoms, or disrupt chemical bonds. When neutrons are absorbed in a nuclear reaction, prompt gammas are emitted and charged particles may be emitted. Additionally the element may be changed when the residual nucleus releases alpha, beta or gamma rays. Since all of these processes can be highly disruptive to chemical bonds, neutrons can cause severe radiation damage.

Gammas and X-rays

Gammas and x-rays are electromagnetic radiation. These photons have no electrical charge and interact with matter differently from particles. Gammas and x-rays are identical in nature, but are different in origin. Gammas are produced in processes that involve the nucleus of an atom, while x-rays are produced by interactions that take place outside of the nucleus. X-rays are emitted with discrete energies or with a broadspectrum of energies, while gammas are always released with discrete energies. In passing through matter, energy is transferred from the incident photon to electrons and nuclei in the target material. An electron can be ejected from the atom with the subsequent creation of an ion. The amount of energy lost to the electron is dependent on the energy of the incident photon and the type of material through which it travels. Gamma and x-ray photons interact with matter in three ways: the photoelectric effect, Compton scattering, and pair production.

Photoelectric Effect

In the photoelectric effect, an incident photon strikes an orbital electron and is totally absorbed by the electron. The electron is then ejected from the atom creating a vacancy in the shell. The ejected electron interacts with other atoms creating ionizations until it loses its kinetic energy. Electrons in the atom drop from the outer shells to fill the vacancy in the inner shell forming characteristic x-rays. Photoelectric absorption occurs predominantly in x-ray photons with energies below 10 keV.

Compton Scattering

Compton scattering occurs when a gamma or x-ray photon scatters from an orbital or free electron. Unlike the photoelectric process, only part of the photon's energy is transferred to the electron. The electron is ejected from the atom and the incident photon is scattered with a reduction in energy. This scattered photon continues to interact with orbital electrons by additional Compton or photoelectric processes. The energy of the scattered beta is the difference between the energies of the original and scattered gammas and x-rays. The probability of Compton scattering increases as the energy of the photon increase. At approximately 35 keV the probability of interactions through photoelectric and Compton collisions are about equal.

Pair Production

In pair production the incident photon must possess a minimum energy of 1.02 MeV. The photon interacts with the electric field around the nucleus and undergoes transformation into matter, with the creation of an electron and positron (positive electron). The original gamma disappears with its kinetic energy shared between the electron and positron. The positron is annihilated in microseconds by interacting with an electron, creating two 0.511 MeV gamma photons (annihilation radiation). These photons then interact with matter by Compton and photoelectric collisions.

5.0 Radiation Measurement

Radiation Units

Roentgen (R)

The roentgen is a unit for expressing exposure from x or gamma radiation in terms of the number of ionizations produced in air. One roentgen of radiation will produce ionizations equal to one electrostatic unit of charge in one cubic centimeter of dry air at standard temperature and pressure.

Rad

The roentgen defines a radiation field in air but does not provide a measure of absorbed dose in ordinary matter or tissue. When radiation passes through an object, part of the energy will be transferred to the material. This is referred to as the absorbed dose. In order that absorption properties of the exposed material be taken into account, a dose unit has been developed called the rad (radiation absorbed dose). In contrast to the roentgen, the rad is used to express the radiation dose absorbed in any medium from any type of radiation. One rad is equal to the amount of radiation that results in the absorption of 100 ergs per gram in any material. It is approximately equal to the absorbed dose delivered to soft tissue by one roentgen of x or gamma radiation.

Rem

In terms of human exposure, however, another factor must be considered; exposure to equal doses from different types of radiation do not result in equal damage to biological tissue. Therefore, in order to account for these varying effects, a unit is used termed the rem (roentgen equivalent man). The rem estimates the amount of any radiation that would be necessary to produce the same biological effects in humans as one rad of x or gamma radiation. The rem is equal to the rad multiplied by a quality factor that estimates the relative biological effectiveness of different types of radiation. This biological effectiveness depends upon the number of ionizations created per unit distance in tissue as the radiation travels through the body. The quality factor for gamma and beta radiation is one, however, quality factors for other types of radiation can be as high as twenty (e.g., alpha, particles). Therefore, a dose of 0.05 rads from alpha particles could do the same biological damage as 1 rad of gamma radiation because both equal one rem (0.05 rads x 20 quality factor). One advantage of using rem units is that dosages delivered from different types of radiation become additive.

In summary, the roentgen is a unit of exposure, the rad is a unit of absorbed dose, and the rem is a unit of biological dose. The rem is the unit that is used to measure radiation doses to personnel. For practical purposes, however, the roentgen, rad, and rem are essentially equivalent for gamma and beta rays and can be used interchangeably. Commonly used subunits are milliroentgen, millirad, and millirem (mR), which are equal to 1/1000 of these units.

International System (SI)

Recently new radiation protection units consistent with the metric system or International System of Units (SI system) have been adopted. In order to phase out the use of the roentgen there is no unit comparable to it in the SI system. The new SI unit for absorbed dose, which replaces the rad, is the gray (Gy). One gray is equal to 100 rads. The new unit for the rem is the Sievert (Sv), which is equivalent to 100 rem. Although SI units are accepted internationally, the roentgen, rad, and rem continue to be widely used in this country.

Maximum Permissible Dose (MPD)

To protect radiation workers and the public, maximum permissible dose limits have been established by the National Council on Radiation Protection (NCRP). The MPD is the dose of radiation, based on current knowledge, that a person can receive without sustaining appreciable bodily injury. The maximum whole-body dose allowed to radiation workers is 5 rem per year or 1.25 rem per quarter. The dose limit to the lens of the eye is 15 rem per year or 3.75 rem per quarter. The dose limit to the skin and extremities is 50 rem per year or 12.5 rem per quarter, reflecting the decreased sensitivity to radiation damage of these areas. Radiation workers under the age of 18 are limited to 10% of these values. The limit for the public has been set at 2 mR/hr or 500 mR/yr. The dose limit for pregnant radiation workers is limited to 500 mR during the course of the pregnancy.

Because any amount of radiation is potentially harmful, the NCRP has officially adopted the ALARA concept. This principal states that all radiation exposures should be kept "As Low As Reasonably Achievable". Maximum permissible doses have been established as reasonable risks comparable to other industries. These doses should be thought of as absolute ceiling levels and not as "safe" limits. Radiation workers should always strive to reduce doses to ALARA levels by using proper safety procedures and techniques.

Survey Instruments

Radiation survey instruments are used to detect radiation contamination, monitor the effectiveness of shielding arrangements, and estimate exposure to personnel. There are two main categories of radiation monitoring devices: gas filled detectors and scintillation detectors.

Gas detection instruments are based on the principle that ions are produced when radiation passes through a gas-filled chamber. Electrons liberated in the chamber are attracted to the center electrode (anode) by a positive voltage potential. Positive ions are attracted towards the walls (cathode) of the chamber. This produces an electrical pulse or current which can be detected and recorded by a scaler or ratemeter.

There are three types of gas filled radiation detectors: ionization chambers, proportional counters, and Geiger-Mueller detectors. The primary difference between these detectors is the voltage applied to the chamber. The kind of detector used is based on the intensity and the type of radiation field encountered. Scintillation detectors operate on the principle that certain materials scintillate or give off light when exposed to radiation. There are two major types of scintillation detectors, crystal and liquid.

Ionization Chambers

At very low applied voltages, ion pairs created by radiation passing through the chamber may recombine before they are collected and counted. As the voltage of a gas filled detector is increased, virtually every ion pair produced by the incident radiation will be captured. The current flowing through the meter is therefore directly proportional to the activity of the source. This feature makes ionization detectors very useful as radiation monitoring devices. Survey instruments operating at this voltage are called ionization chambers or "cutie pies". Because almost all ion pairs are collected, this instrument is used when it is necessary to accurately determine exposures. Ionization chambers, however, are relatively ineffective for measuring rates less than 1 mR/hr, and are slow to respond to changing fields. For this reason ion chambers are not useful for detecting contamination and are primarily used to determine exposures in areas of high radiation intensity.

Proportional Counters

As the voltage of the tube is increased, electrons are accelerated faster and achieve sufficient energy to create secondary ionizations in the gas. This amplification is termed an avalanche and dramatically increases the size of the electrical pulse at the central anode. Gas multiplication can create millions of ion pairs per ionizing event, in contrast to the ionization chamber which creates one ion pair. Although an avalanche has occurred, gas amplification is proportional to the energy of the initiating event in this voltage region. Radiation monitoring devices operating in this region are called proportional counters. With sufficiently thin windows alpha particles, which produce a large number of ions in the gas, can be distinguished from beta particles. In addition, the counter can be used to measure the energies of incoming gamma rays.

A portable gas flow proportional counter that is often used in laboratories to detect contamination is called a PAC-4G. Its range is from zero to 500,000 counts per minute(cpm). The detector is a large flat rectangular area that provides great sensitivity. The PAC-4G can detect beta energies as low as C-14 but not H-3. The instrument can also detect contamination from alpha particles.

Geiger-Mueller (GM) Counters

The GM counter is the most widely used area survey instrument for the detection of low-level radioactive contamination and exposure. It is very sensitive, relatively inexpensive, and rugged. Radiation passing into a GM tube (typically containing helium, neon, or argon) creates ions that are accelerated by a high voltage potential of approximately 1200 volts. Secondary ionizations are created from collisions with the accelerated ions. These ions are also accelerated and achieve sufficient energy to form additional ions. This process eventually produces an avalanche of billions of ion pairs from the initial ionization and creates a large electrical pulse at the anode. The magnitude of the output pulse is independent of the nature of the particle or its energy because gas amplification has reached its maximum potential.

A major disadvantage of GM counters is their limitation to low radiation fields, typically below 200 mR/hr. Once ionizations have been initiated in a GM tube it becomes insensitive for a short time, called the dead time, and will not respond to further ionizing events. As a result, the number of counts recorded will be less than the true count rate. This error is relatively small at low radiation intensities, however, in high radiation fields large errors can be introduced. At very high exposure rates, where events are interacting with the tube much faster than the dead time, the counter may actually saturate and read zero.

With sufficiently thin windows, alpha, beta and low energy gamma rays can be detected. A typical GM counter can be used to count either betas or gammas. The betas enter the gas through a fragile thin window, typically located at the end of the cylinder. The window is as thin as 1.5 mg/cm2. The counter can detect betas with energies as low as 0.030 MeV and even some alphas. If the window is covered by a shield to prevent charged particles from entering, the response of the counter can be limited to gammas. This permits characterization of the radiation field. Betas from H-3 cannot be adequately monitored by any gas filled devices because of their very low energies.

Detector can be purchased in the following configurations: side window, thin end window or a pancake type window. The side window detector has a relatively thick window which the radiation must penetrate. Typically, betas of less than 200 KeV are not energetic enough to be detected, and alphas cannot penetrate the window. This detector would not be satisfactory for H-3, C-14 or S-35, since their beta energies do not exceed 200 KeV. The 1.71 MeV betas of P-32 could be detected but other probes are normally used. This type of detector is effective for gammas with energies greater than 50 KeV. Betas and gammas can be differentiated by sliding a built-in metal shield over the window to completely block out the betas.

The next detector uses a thin end window. Betas with energies as low as 40 KeV can be detected. This detector can be used to detect the betas from C-14, S-35 and P-32 with efficiencies ranging from 10% (C-14) to 40% (P-32). Betas from H-3 cannot be detected. Alphas with energies greater than 4 MeV are detectable. Some beta/gamma discrimination can be achieved by covering the window with a shield which only gammas can penetrate.

The last type of GM detector uses a large pancake shaped probe. This probe will detect alphas, betas and gammas similar to the thin end window detector. The pancake probe has a greater sensitivity than the end window type because the probe's active surface area is about 3 times larger than the end window.

Scintillation Detectors

Scintillation detectors use a crystal that releases light when exposed to x-rays or gamma rays. There are two types of scintillation detectors; solid and liquid. Most solid scintillation crystals are composed of sodium iodide with a small amount of thallium added as an "activator". The crystal is coupled to a photomultiplier tube that converts the light flashes to amplified electrical pulses. Amplification factors of a million or more are achieved. The number of pulses are directly proportional to the intensity, and the size of the pulse is directly proportional to the energy of the incident radiation. These pulses are then analyzed by a counter, spectrometer, oscilloscope, or computer.

Because scintillation crystals are solid, rather than gaseous, their higher density and atomic number makes them very efficient and sensitive instruments for the measurement of x-rays and gamma rays. Portable scintillation detectors are even more sensitive than GM counters because of their increased efficiency. The crystal in a solid scintillation detector can be thin or thick. The thin crystal has an energy range of approximately 10-60 KeV, while the thick crystal has a range from about 50 KeV to 1 MeV. Scintillation detectors, however, are not as rugged as Geiger counters because the crystal is hygroscopic and can absorb water from the atmosphere.

Liquid scintillation detectors use organic compounds that give off light when radioactive materials are added to a liquid scintillation cocktail (LSC). Material from a swipe is dissolved or suspended in the solution, and almost all of the emitted radiation passes through some portion of the scintillator. The light is detected by photomultiplier tubes and analyzed and counted in a manner similar to solid scintillation detectors. The liquid scintillation counter is primarily used for detection of beta contamination. Detection efficiencies range from approximately 40% (H-3) to almost 100% (P-32). The instrument can also detect alphas (up to 100% efficiency) or gammas (up to 20% efficiencies).

Radiation Monitoring Techniques

Two types of instruments are commonly used to monitor contamination of personnel, equipment, and areas. Portable survey instruments provide direct measurement capabilities. Fixed instruments such as liquid scintillation counters provide an indirect means to determine contamination by analyzing paper wipes of test areas. While portable instruments are faster, fixed instruments offer greater sensitivity.

Before a portable survey instrument is used, several quality checks should be made. The calibration sticker should be checked to ensure that the instrument is not due for recalibration. The batteries should be checked to ensure the instrument will be powered properly. Finally, the instrument response should be tested with a check source.

Most instruments have a response time selector. This will vary the response from slow (10-15 seconds to reach 70% of true readings) to fast (1-3 seconds). The fast response times will greatly reduce the survey time. After the proper response time is selected, turn on the instrument to its most sensitive scale (e.g. X1 or X0.1) and determine the background readings for that scale. Once the background is determined, the monitoring must be performed slowly at a rate of approximately 1 inch per second and very close to the surface without touching. If the probe has a window, this must be directed at the surface being monitored. However, small or pointed objects can puncture the thin windows if care is not used. If a reading above background is indicated, the probe movement should be stopped to determine the extent over background. The response time should be changed to slow to get a more accurate reading. Since the clean limit is 220 DPM, the actual value can be calculated as follows:

  • gross CPM - background CPM = net CPM
  • net CPM/Efficiency= DPM note: (10% = 0.1 divisor)

The other method of monitoring uses paper wipes that are analyzed in a fixed instrument such as a liquid scintillation counter (LSC). A piece of dry filter paper is rubbed on the area to be tested, using moderate pressure. An area of 100 square centimeters (16 square inches) should be tested. The filter paper is placed in a LS vial, fluid added, and counted. The results are calculated in the same manner as the portable instrument except counting efficiencies are usually much higher.

Personnel Monitoring

Personnel monitoring is used to detect and measure radiation exposure to workers. The purpose of personnel monitoring is to document the exposure an individual receives to determine if radiation limits have been exceeded, and to aid in keeping doses as low or reasonably achievable. Personnel monitors are relatively inexpensive, reasonably reliable, and portable. They are usually worn on the belt, shirt pocket, collar, or finger. Personnel monitoring devices designed to measure low energy radiation should not be worn in a shirt pocket.

Personnel monitoring is required if there is a possibility that a radiation worker will receive greater than 10% of the maximum permissible dose (MPD).

Film Badges

The film badge consists of one or more photographic emulsions contained in light tight envelopes inside a plastic holder. These emulsions have varying degrees of sensitivities to x-rays, gamma rays, beta particles, and neutrons. Windows and filters are built into the badge to distinguish between different types of radiation. An estimation of radiation energies can also be made. The film is developed and the density of the exposed film is proportional to the exposure received by the film badge. The degree of darkening is compared with film exposed to known quantities of radiations. Film can also discriminate between primary beam exposure and scattered radiation. Scatter radiation produces a fuzzy image while a distinct image is produced from primary beam exposure.

Film badges have several advantages that have made them the most popular form of personnel monitoring devices. They are inexpensive, reasonably accurate and sensitive, provide a permanent record of exposure, and supply information on the type and approximate energy of the radiation exposure.

Film badge monitors also possess several disadvantages that have led to a decline in their popularity. Film badges are not as accurate or reliable as other personnel monitoring devices, nor do they detect exposures from low energy photons very well. In addition, film badges are relatively insensitive, the lower limit of detection is typically between 20 to 30 mR. Artificially high readings can result from false darkening as a result of improper handling, heat, humidity and age. In order to limit false darkening, film badges should not be worn for periods in excess of a month.

Pocket Dosimeters

Pocket dosimeters are small, pencil shaped ionization chambers that directly measure ionizations due to radiation. The chamber is charged before use and a scale is adjusted to read zero at this voltage potential. As radiation passes through the chamber, ions are created. These ions are collected at the electrodes of the chamber and discharge the dosimeter. This discharge is directly proportional to the quantity of radiation entering the chamber and read on a voltage meter that is calibrated in radiation units. Some pocket dosimeters can be read directly from an internal scale while others must be inserted into a dosimeter reader.

The major advantage of a pocket dosimeter is its ability to supply an immediate readout of radiation exposure. Because of this, pocket dosimeters are typically used only in high radiation area. It is important to ensure that the dosimeters can detect the energy of the radiation field being emitted. Pocket dosimeters are also reasonably accurate and sensitive, however, they are expensive, easily damaged, and give false readings due to charge leakage.

Thermoluminescent Dosimeters

The newest type of personnel monitoring device, which is rapidly becoming the most popular, is the thermoluminescent dosimeter (TLD). This device looks similar to a film badge but uses a calcium fluoride or lithium fluoride crystal to measure radiation exposure. When radiation strikes the crystal, electrons absorb the energy and are promoted to higher energy states in the crystalline lattice. Upon heating, these excited electrons fall back into their original energy states releasing the stored energy as ultra-violet light. The amount of this light is directly proportional to the radiation dose received by the crystal. The light is then quantified by a photomultiplier tube.

TLD monitors have several advantages and few disadvantages. They are more accurate, reliable, and sensitive than film badges and pocket dosimeters, and their response to low as well as high energy photons is more uniform. TLD monitors are also relatively sensitive; radiation doses as low as 5 mR can be detected. TLD monitors are not influenced by normal heat and moisture, which allows the monitors to be worn for as long as three months without loss of information. TLD monitors are also reusable, having lost the "memory" of the previous radiation exposure when heated. They can also be read quickly so that radiation doses can be obtained within a few minutes.

The primary disadvantage of TLD monitors is cost. The monitoring program can be twice as expensive as film badge monitoring. However, this cost can be reduced because TLD monitors can be read every three months instead of monthly. Costs are expected to be lowered in the future and TLD monitors will probably replace film badges as the method of choice in personnel dosimetry programs.

6.0 Reducing Radiation Exposure

Because any amount of radiation is potentially harmful every effort should be made to reduce doses to a level that is as low as reasonably achievable. Time, distance, shielding, and substitution represent four practical methods laboratory personnel can use to minimize external radiation exposure.

Time

The dose of radiation received is directly proportional to the amount of time spent in a radiation field. Thus, reducing the time by one-half will reduce the radiation dose by one-half. Users should always work quickly, efficiently and spend as little time as possible around radioisotopes. Personnel can reduce time by ensuring that all tools and materials are in place before the radioactive material is brought out of storage. The use of practice runs without radioactive materials is also recommended to increase familiarization with the technique and increase operator speed.

Distance

Radiation exposure decreases rapidly as the distance between the worker and the radiation source increases. Maximizing distance represents one the simplest and most effective methods for reducing radiation exposure to workers. For example, distance can be maximized by using long handled tools to keep radioactive materials well away from the body and storing radioactive materials as far from workers as possible.

The decrease in exposure from a point source of x or gamma radiation can be calculated by using the inverse square law. This law states that the amount of radiation at a given distance from a point source varies inversely with the square of the distance. For example, doubling the distance from a radiation source will reduce the dose to one-fourth of its original value, and increasing the distance by a factor of three will reduce the dose to one-ninth of its original value. For example, if the dose rate at one foot from a source is 20 mR/hr, then the dose rate at two feet (twice the distance) will be 5 mR/hr.

In contrast to x or gamma radiation, beta particles have a finite range in air. Low energy beta emitters such as H-3, C-14, S-35 do not pose an external radiation exposure problem when the material is handled in containers. Higher energy beta emitters such as P-32 do pose an external hazard. Since the energy distribution of betas is from zero to some maximum (dependent upon the isotope), the average energy is approximately one-third of the maximum. Once the distance from a beta source exceeds 4 inches, dose rate reduction follows the inverse square law as the separation distance increases.

Shielding

Radiation exposure can also be decreased by placing a shielding material between a worker and the source of radiation. Materials with high densities and high atomic numbers are the most effective shielding choice for protection from x and gamma rays. The energy of the photons is reduced by Compton and photoelectric interactions in the shielding material. Thus, substances such as lead, concrete, and steel are very practical shielding materials because of the abundance of atoms and electrons that can interact with the photon. As the energy of the gammas increase, the thickness of shielding must increase to provide comparable stopping power. The amount of shielding necessary to reduce the radiation intensity to a desired level can be calculated from the half-value layer of the material. The half-value layer is the thickness of the material necessary to reduce the radiation intensity to one-half of its original value. Seven half-value layers will reduce the radiation level approximately 100 times, and ten half-value layers will reduce the radiation level by a factor of 1000.

An example of a shielding device for gammas is a benchtop shield. The upright portion shields the whole body while an angled top piece of leaded glass shields the face. This angled top feature allows for optimum viewing while keeping exposures low. This type of shield should be used when stock solutions of gamma emitters such as Zn-65 or Fe-59 are manipulated. When low energy gamma emitters such as I-125 are used, lead foil can effectively reduce the emissions.

The shielding principles applied to beta particles are different from those applied to x and gamma rays. Since beta particles have a finite range, shields are designed to totally stop all betas. While gamma shields rely on high density, beta shielding materials must be made from low density materials. The incidence of "bremsstrahlung" increases to unacceptable levels if beta shields are composed of materials with an atomic number higher than aluminum (13).

Bremsstrahlung results in the conversion of beta energy into x-rays and these secondary x-rays can pose a greater hazard than the original betas. For this reason beta shields are commonly composed of plexiglass, glass, aluminum, or water. Plexiglass bench top shields provide protection for the body and eyes and plexiglass or aluminum blocks are used as tube holders to protect the hands. Several thicknesses of tygon tubing provide excellent hand shielding when a tube must be held. Plexiglass cylinders or PVC pipe can shield liquid waste or other containers of radioactive solutions.

Substitution

The isotope selection process is another effective method to reduce potential radiation exposures. The areas to be considered are: the radioactive half-life, the energy and type of emissions, the quantity of isotope, and the chemical form of the isotope. The half-life of the isotope selected can affect waste management. Generally, shorter lived isotopes are preferred over longer lived. Since the University stores waste with half-lives less than 90 days until decayed to background, this category of waste causes minimal monetary impact because it is not shipped. This waste also poses minimal environmental impact because it is not sent to a radioactive waste burial facility.

The energy and type of emissions from the perspective isotopes must be considered. Selection of low energy beta or gamma emitters is preferred because radiation hazards are proportionally related to the energy. Beta emitters are preferred over gamma emitters because betas require less shielding. The radiation hazard is also proportionally related to the quantity (radioactivity) of the isotope to be used. The use of small activities is preferred. The chemical form selected for the experiment can also affect the radiation hazards associated with the work. It is preferred to avoid the use of compounds that are or produce volatile or gaseous compounds.

Several examples can be used to illustrate the selection process. When considering the use of phosphorus, two isotopes are feasible. P-32 has a short 14 day half-life but emits high energy betas (1.710 MeV). P-33 has a longer half-life (25 days) but emits low energy betas (0.248 MeV). P-33 would be the most desirable isotope to use, however, availability is limited. Recently, a substitute for P-32 has been found for use in a number of molecular biology procedures. The substitute is S-35, with its 87 day half-life and low 0.168 MeV beta. The low energy improves resolution of autoradiographs and requires no shielding or remote handling.

A common use of iodine involves studies with iodinated hormones. Two isotopes of iodine, I-125 and I-131, are feasible. The low x and gamma radiation of I-125 makes it more acceptable than I-131 (high beta and gamma emitter).

Exposure of the human body to ionizing radiation can result in harmful biological effects. The nature and severity of the effects depends primarily on the dose of radiation absorbed and the rate at which it is received. Exposure to radiation can result in radiation burns and sickness, cancer, genetic defects, and abnormalities in unborn children. Very large doses of radiation to the whole body can result in death. These effects have been observed in people exposed to radiation in a variety of situations including therapeutic x-rays, radiation accidents, and the Japanese A-bomb survivors.

Radiation Burns

Radiation burns were first noted within a month of Roentgen's discovery of x-rays. Within a year, it was widely known that radiation workers had to take precautions to avoid injury. Today, great efforts are made to protect workers from accidental exposure but radiation induced injuries still occur. Severe local injury may result when a worker is exposed to a high dose of radiation for a short period of time. Symptoms may range from reddening of the skin, swelling and blistering, to tissue death and amputation of the affected area.

For example accidental exposure to the primary beam from analytical x-ray equipment may result in high radiation doses to localized areas of the body. The smallest dose to the skin that will result in visible damage is approximately 300 rem. Reddening of the skin, called erythema, may occur 2-3 weeks after the exposure in highly susceptible individuals. Usually the dose must exceed 600 rem before radiation burns become apparent. These burns are equivalent to first-degree thermal burns similar to a mild sunburn. There are no initial symptoms from the over-exposure and the worker may be unaware of an injury. These types of injury, however, are typically not seen in radioisotope laboratories.

Radiation Sickness

Radiation burns occur when a large dose of radiation is received by a small part of the body. Severe damage and tissue death may occur but the exposed person usually survives. If a large dose of radiation is delivered to the whole body of an individual in a short period of time, severe illness or death may occur. The sequence of events that follows exposure to high levels of radiation to the whole body is termed radiation sickness or the "acute radiation syndrome".

Radiation doses to the whole body greater than 100 rem delivered within a few hours, are usually necessary to produce noticeable symptoms. Changes in the blood, however, can be observed from exposures as low as 25 rem. Symptoms usually become apparent within a few hours or days depending on the dose received. The first stage of radiation sickness is often characterized by nausea, vomiting, and diarrhea. Following this initial period of sickness, symptoms may subside and the individual may feel well. This stage can last from hours to weeks, and while no symptoms are present, changes are occurring in the internal organs.

Following this asymptomatic period, other symptoms may appear. Loss of hair and appetite, fatigue, fever, severe diarrhea, vomiting, internal bleeding, and death may occur, depending on the dose received. If a whole-body dose of 400-500 rem is received, approximately 50% of those exposed will die within 30 days if untreated. Recovery is likely with medical care although the exposed individual will suffer several months of illness. If the radiation dose is spread over several weeks, a person may survive a whole-body dose or large as 1000 to 2000 rem. Exposure to a dose in excess of 700 rem to the entire body in a short period of time will likely result in death within a few weeks. This dose of radiation kills cells in the bone marrow and the body can no longer produce enough red blood cells to survive. Doses of the magnitude necessary to cause radiation sickness are not typically seen in radioisotope laboratories.

Cancer

Exposure to chronic small doses of radiation over long periods of time can result in delayed effects that may become apparent years after the initial exposure. These effects may also occur after acute exposure to high doses and include carcinogenesis, life span shortening, and cataract formation.

The principle delayed effect from chronic exposure to radiation is an increased incidence of cancer. Ionizing radiation is a well known carcinogenic agent in animals and humans and has been implicated as capable of inducing all types of human cancers. Those types of cancer with the strongest association with radiation exposure include leukemia, cancer of the lung, bone, female breast, liver, skin, and thyroid gland.

By 1905 it was widely known that exposure to radiation could cause cancer. Many of the early researchers who were exposed to large repeated doses of radiation died from fatal skin cancer and leukemia. Marie and Pierre Curie, for example, both developed leukemia, probably from their experiments with radium.

Further evidences that ionizing radiation can induce cancer in humans has been demonstrated among radiation workers, children exposed in-utero to diagnostic x-rays, patients receiving therapeutic x-rays and internal radiation exposure, individuals exposed to fallout, and the Japanese A-bomb survivors. Some of these evidences are summarized below:

  1. Increased incidences of cancer have been noted among several groups of radiation workers exposed to high doses. Among these were the early radiologists, uranium miners, and radium watch dial painters. The early radiologists were often exposed to large doses of radiation without the benefit of protective devices. Many developed cancerous skin lesions on the hands and suffered from radiation burns. Higher incidences of leukemia were also demonstrated in this group. In the early 1900's, 50% of the uranium miners in some European mines died from lung cancer. Radium-dial painters at the beginning of this century, hand painted the luminous numerals on watches and clocks with a paint containing radium. The workers would put the brush on their lips to draw the bristles to a fine point. Increased incidences of bone cancer and other malignancies were seen in these workers.
  2. Increased incidences of cancer have been demonstrated from exposure to diagnostic x-rays. Children exposed to radiation as a result of abdominal x-rays to the mother during pregnancy have shown as increase in leukemia. An increase in breast cancer was noted among women with tuberculosis who received repeated fluoroscopic examinations.
  3. Exposure to therapeutic x-rays has resulted in increased incidences of cancer among patients treated for scalp ringworms, arthritis of the spine, and enlargement of the thymus glands. To reduce the size of the thymus gland, for example, doses of 120 to 6,000 rad were often given to infants. Increases were seen in thyroid cancer and leukemia.
  4. Mortality from liver cancer was increased among patients who received a radio-contrast material, Thorotrast. This compound contained thorium, a naturally occurring alpha emitting radioisotope.
  5. Increased incidences of thyroid cancer were demonstrated in residents of the Marshall Islands who were accidently exposed to radioactive fallout from a nuclear bomb test. Children in Utah and Nevada exposed to fallout in the 1950's also demonstrated increases in thyroid cancer.
  6. The strongest evidence for radiation induced carcinogenesis in humans has come from studies of the Japanese A-bomb survivors. These data have suggested that radiation may be a general carcinogenic agent capable of inducing all types of cancers. Increased incidences of leukemia, cancer of the breast, respiratory organs, digestive organs, and urinary organs have been reported. In addition, the data has demonstrated a linear relationship between dose and radiation induced leukemia.

It is not known how radiation induces cancer. Several theories have been proposed to explain the carcinogenic properties of radiation. Cancer is characterized by the uncontrolled growth of cells. According to one theory, radiation damages the chromosomes in the nucleus of a cell resulting in the abnormal replication of that cell. Another theory postulates that radiation decreases the overall resistance of the body and allows existing viruses to multiply and damage cells. A third theory suggests that as a result of irradiation of water molecules in the cells, highly reactive and damaging agents called "free radicals" are produced which may play a part in cancer formation.

Approximately 25% of all adults between the ages of 20 and 65 will develop cancer during their lifetime. It is not known what an individual's chances are of developing cancer from exposure to ionizing radiation. However, risk estimates can be made based on statistical increases in the incidence of cancer among populations exposed to large doses of radiation.

The Nuclear Regulatory Commission (NRC) has adopted a linear, non-threshold model for calculating the cancer risks associated with low level radiation exposure. According to the NRC, this model neither seriously underestimates nor overestimates the risks involved from radiation exposure. Using this model, the risks decrease proportionally to the does of radiation. Thus, a worker who receives 5,000 mR/yr is assumed to incur ten times the risk as a worker who receives 500 mR/yr. Because no threshold is assumed, theoretically all radiation exposures have the potential to cause cancer. Based on this model, the best risk estimates available today are that an additional 3 cancers would occur in a group of 10,000 radiation workers exposed to 1,000 mR each. This should be compared to the 2,500 cancer cases that would be expected to occur from other causes. It is important to realize that these risk estimates are extrapolated from high doses and may not apply to low doses. Increases in cancer have not been clearly demonstrated at levels below the occupational limit of 5,000 mR/yr.

Recent controversial studies have suggested that linear extrapolation from high doses may significantly underestimate the actual risks involved from chronic low doses of radiation. Other studies have indicated that extrapolation may overestimate these risks. Both sets of data, however, lack sufficient validity to be used with confidence for the estimation of cancer risks at this time.

Genetic Effects

Radiation exposure to the reproductive cells can alter the genetic code, resulting in damaged or defective genes that can be passed on to future generations. It has been known since 1927 that radiation can cause genetic defects in the descendants of insects. Experiments with other animals have shown similar results. These studies demonstrated that radiation does not increase the types of mutations seen in nature, only the frequency.

Genetic mutations, however, have not been demonstrated in human populations exposed to radiation. For example, studies of the children of the A-bomb survivors in Japan have not detected any more genetic defects than expected. It is very difficult to determine if a person has a particular genetic defect. Usually there are no easily detectable signs and several generations and large populations may be necessary before the mutation becomes visible. Most effects will probably be seen in subsequent generations as minor impairments that lead to higher spontaneous abortions, shorter life spans, increases in diseases, and ill health. Serious genetic defects usually do not manifest themselves because the person does not survive to reproduce.

Based on the irradiation of animals, the following inferences can be made regarding genetic effects in humans:

  1. Radiation is a powerful mutagenic agent and any amount of radiation can potentially damage a reproductive cell.
  2. The vast majority of genetic mutations are recessive. Both a male and female must possess the same genetic alteration in their chromosomes in order for the mutation to be expressed.
  3. Most genetic mutations are harmful and decrease the overall biological fitness of a species.

Because genetic mutations are usually undesirable, the level of genetic defects in the population should be kept as low as possible. This can be accomplished by avoiding any unnecessary radiation exposure.

The risk of a genetic defect in a child of a person exposed to one rem of radiation is approximately one-third that of developing cancer. Thus, there would be about one chance in 10,000 that the child would have a genetic defect. Because genetic defects are less likely than cancer, and not as serious, the risk of developing cancer from radiation exposure is more significant.

Teratogenic Effects

Radiation exposure to a pregnant woman may be harmful to the unborn child. Malformations induced in the embryonic or fetal stages of development are termed teratogenic effects. Embryological and fetal tissue are composed of rapidly dividing unspecialized cells that are highly sensitive to damage from ionizing radiation. Radiation exposure in-utero can result in spontaneous abortions, congenital abnormalities, impairment of growth and mental functions, and increased incidences of leukemia.

The effects of radiation exposure during pregnancy are dependent on the stage of pregnancy and the dose of radiation received. The most critical stage of pregnancy is the first trimester. This includes the time a woman may not even be aware she is pregnant.

During this period, rapid cell division is occurring and the major body organs are forming. Exposure during the first trimester may result in embryonic death or congenital malformations. During the later stages of fetal growth, functional changes such as learning disorders or leukemia are possible. As the fetus ages, however, it becomes more resistant to radiation.

Evidences of embryological and fetal effects in humans have been demonstrated in the Japanese A-bomb survivors and children exposed to diagnostic x-rays while in-utero. An increase in mental retardation and small head circumference was observed in the children of the A-bomb survivors. Irradiation of the fetus from diagnostic x-rays has been associated with an increased incidence of leukemia in children. The highest risk occurred to those x-rayed during the first trimester. Because of the sensitivity of the developing fetus to radiation, a pregnant radiation worker should limit her whole-body exposure to 500 mR during the course of the pregnancy.

Conclusion

The health risks associated with exposure to ionizing radiation are smaller that the risks involved in many of our daily activities. These risks are also comparable to those encountered in other professions. This small but real increase in health risks calls for a weighing of the benefits versus the risks associated with the use of radiation. Radiation workers are benefited because their livelihood is derived from the use of radiation and students and researchers receive the benefit of a valuable educational and research tool. However, if the same information can be obtained by using methods that reduce the exposure and risks then they should be employed. Because the biological effects of exposure to low level ionizing radiation are not fully understood, it is prudent to maintain radiation doses at a level that is as low as reasonably achievable (ALARA concept).

Glossary

Activity: the number of atoms decaying per unit of time.

Airborne radiation area: any room, enclosure, or operating area where airborne radioactive materials exist in concentrations above the maximum permissible concentration (MPC) specified in 10 CFR 20; or any room enclosure or operating area where airborne radioactive material exists in concentrations that, averaged over the number of hours in any week when individuals are in the area, exceed 25% of the MPC's specified in 10 CFR 20.

Alpha particle: a helium nucleus consisting of two neutrons and two protons, with a mass of 4 AMU and a charge of +2.

As low as reasonably achievable (ALARA): basic radiation protection concept to reduce doses to the lowest possible levels through the proper use of time, distance and shielding.

Atom: the smallest division of matter that still displays the chemical properties of an element.

Atomic mass unit (AMU): one twelfth of the arbitrary mass assigned to carbon 12. It is equal 1.6604 x 10 24 gm.

Becquerel: a unit of activity equal to one disintegration per second.

Beta particle: a charged particle emitted from the nucleus of an atom, with a mass and charge equal to that of the electron.

Bremsstrahlung: German for braking radiation. It is incidental photon radiation caused by the deceleration of charged particles passing through matter.

Chain decay: a process by which an unstable atom decays to another unstable atom, repeating the process until the atom becomes stable.

Code of Federal Regulations (CFR): title 10 contains the regulations established by the NRC. Part. 19 deals with the rights of employees to be informed of any radiation hazards associated with their working conditions, and the rights of the worker to complain about any working conditions that may be unsafe. Part. 20 is the basic regulatory guide which establishes the standards for protection against ionizing radiation.

Compton scattering: interaction process for x or gamma radiation where an incident photon interacts with an orbital electron of an atom to produce a recoil electron and a scattered photon with energy less than the incident photon.

Curie: a unit of activity equal to 3.7 E10 disintegrations per second.

Decay, radioactive: the disintegration of the nucleus of an unstable atom caused by the spontaneous emission of charged particles and/or photons.

Electron: elementary particle with a unit negative charge and a mass of 1/1840 AMU.

Energy shells: labels given to the different orbits of the negatively charged electrons circling the nucleus of an atom.

Gamma: electromagnetic radiation with a very short wave length and no mass or charge.

Half-life: the time required for the initial activity to decrease by half.

High radiation area: any area accessible to personnel where there exists radiation at such levels that a major portion of the body could receive a dose over 100 mR in any one hour.

Isotopes: atoms with the same number of protons, but different numbers of neutrons.

Monoenergetic: where all the particles or photons of a given type of radiation (alpha, beta, neutron, gamma, etc.) originate with and have the same energy.

Neutrino: a particle with no mass or charge, but has energy associated with it.

Neutron: an atomic particle with a mass of 1 AMU and no charge.

Nuclear Regulatory Commission (NRC): Federal agency charged with the responsibility of regulating the use of radioactive material.

Nucleus: the central part of an atom that has a positive charge, and is composed of protons and neutrons.

Pair production: an absorption process for x and gamma radiation where the incident photon is annihilated in the vicinity of the nucleus of the absorbing atom, producing an ion pair (beta and positron). This process only occurs for incident photon energies exceeding 1.02 MeV.

Photoelectric effect: process by which a photon ejects an electron from an atom. All the energy of the photon is absorbed in ejecting the electron and in imparting energy to it.

Photon: energy emitted in the form of electromagnetic radiation, such as x-rays and gamma rays.

Positron: particle equal in mass to the electron and having an equal but positive charge.

Proton: a particle with a positive charge and a mass of 1 AMU.

Quality factor: a term to express the varying effects of different types of radiation when assessing doses to tissue.

Rad: an amount of absorbed radiation dose of 100 ergs per gram of matter.

Radiation area: any area accessible to personnel where there exists radiation at such levels that a major portion of the body could receive a dose of over 5 mR in any one hour or a dose over 100mR in any 5 consecutive days.

Rem: stands for radiation equivalent man, the dose in rems is equal to the dose in rads multiplied by the quality factor.

Restricted area: any area where access is controlled by the University to protect individuals from exposure to radiation and radioactive materials.

Roentgen: the amount of x or gamma radiation which will cause ionization of one electrostatic unit of charge in 1 cubic centimeter of dry air at standard temperature and pressure.

Specific activity: total activity of a given nuclide per gram of a compound, element, or radioactive nuclide.

Tenth value: the thickness of a given material that will decrease the amount of radiation to one-tenth of the original value.

X-ray: penetrating electromagnetic radiation similar to visible light, but having extremely short wave lengths.

Commonwealth of Virginia Department of Health

NOTICE TO EMPLOYEES

Standards for protection against radiation notices, instructions and reports to workers, inspections.

Your employer's responsibility

Your employer is required to:

  • Apply these Department of Health Regulations and any conditions of his radioactive materials license to all work involving radiation sources.
  • Post or otherwise make available to you a copy of the regulations, licenses and operating procedures which apply to work you are engaged in, and explain their provisions to you. Copies may be obtained from the Radiation Safety Office.
  • Post Notice of Violation involving radiological working conditions, proposed imposition of civil penalties and orders.

Your responsibility as a worker

  • Limits on exposure to radiation and radioactive materials in restricted and unrestricted areas
  • Measures to be taken after accidental exposure
  • Personnel monitoring, surveys and equipment
  • Caution signs, labels and safety interlock equipment
  • Exposure records and reports
  • Related matters

Reports on your Radiation exposure history

The Department of Health regulations require that your employer give you a written report if you receive an exposure in excess of any applicable limit as set forth in the regulations or in the license. The basic limits for exposure to employees are set forth in Section D.101, D.103 and D.104 of the regulations. These sections specify limits on exposure to radiation and exposure to concentrations of radioactive material in air and water.

If you work where personnel monitoring is required pursuant to Section D.202:

  • Your employer must give you a written report of your radiation exposure upon the termination of employment if you request it.
  • Your employer must advise you annually of your exposure to radiation.

Inspections

All licensed or registered activities are subject to inspection by representatives of the Department of Health. In addition, any worker or representative of workers who believes that there is a violation of the Rules and Regulations for Ionizing Radiation or the terms of the employer's license or registration with regard to radiological working conditions in which the worker is engaged may request an inspection by sending a notice of the alleged violation to the Bureau of Radiological Health. The request must set forth the specific grounds for the notice, and must be signed by the worker or the representative of the workers. If requested, anonymity will be maintained. During inspections agency inspectors may confer privately with the workers and any worker may bring to the attention of the inspector any past or present condition which he believes contributed to or caused any violation as described above. No licensee or registrant shall discharge or in any manner discriminate against any worker because such worker has filed any complaint or instituted or caused to instituted any proceeding under these regulations or has testified or is about to testify in any such proceeding or because of the exercise by such worker on behalf of himself or others of any option afforded by this part.

Inquiries

Inquiries dealing with matters outlined above can be sent to the Bureau of Radiological Health, 910 James Madison Building, 109 Governor Street, Richmond, Virginia 23219, Telephone 800-786-5932 or the Radiation Safety Office, Radford University, Radford, Virginia 24142, Telephone 540-831-5860.