Radiation Safety

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.

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
• 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.

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.