Chapter 3: Radiation Protection Principles
External doses can be the result of exposure to gamma, x-ray, or high-energy beta emitters. Low energy beta and alpha emitters lack the energy needed to penetrate the outer layer of skin and subsequently present less of an external hazard, and are of more concern when ingested. The radiation dose an individual receives depends on the following factors:
Exposure: The “strength” (activity, mrem/hr, etc.) of the radiation source. By reducing the amount of radioactive material used or lowering the settings on a radiation-producing machine, dose can be reduced.
Time: The total dose received from an external source is dependent on the amount of time actually exposed to the source. Therefore, any time that is spent near a source should be controlled, and used effectively.
Distance: By increasing the distance between the source of exposure and an individual, the dose received can be significantly reduced. When an individual doubles his/her distance from a gamma source, for example, the dose rate at the further distance will drop to one-fourth of the level at the closer distance.
Shielding: When radiation sources are being used, absorbing material or shields can be incorporated to reduce exposure levels. The specific shielding material and thickness is dependent on the amount and type of radiation involved.
Internal exposure results from the absorption, ingestion or inhalation of radioactive material. This material can be incorporated in the body in several ways:
- Breathing radioactive gases, vapors or dust.
- Consuming radioactive material transferred from contaminated hands, tobacco products, food, or drink.
- Entering through a wound.
- Absorption through the skin.
Fundamental objectives of radiation protection measures
- To limit exposure from external radiation to levels that are as low as reasonably achievable and always within the
established dose limits.
- To limit entry of radionuclides into the human body via ingestion, inhalation, absorption, or through open wounds when unconfined radioactive material is handled, to quantities as low as reasonably achievable and always within the established limits.
When these objectives have been met, it is practicable to use radiation sources for academic, development, research and clinical procedures.
- The procedure for each project should be well outlined in writing for all laboratory personnel. Necessary equipment, waste containers, and survey instruments must be available.
- Characteristics of the radioactive material such as type of radiation, energy, half-life, significant and typical amounts, and chemical form should be known.
- In some cases, before the procedure is actually performed with radioactive material, a “dry run” practice of the procedure may be useful to avoid problems.
- A radiation worker should supervise visitors and students in a laboratory that uses radioactive material.
- Radioactive material must not be left unattended in places where it may be handled or removed by unknowing and unauthorized persons. All lab rooms and waste storage areas must be locked when unattended.
- As a general practice, work with radioactive material should be confined to only the areas necessary. This simplifies the problem of confinement and shielding, and aids in limiting the affected area in case of an accident.
- All work surfaces and storage areas (tabletops, hoods, floors, etc.) should be properly covered. Some facilities, especially in older buildings, are very difficult to decontaminate.
- Absorbent mats or paper should be used. Protective absorbent with a plastic back and absorbent front is especially useful. If contaminated, it can simply be discarded in the radioactive waste container.
- Plastic or metal trays (stainless steel washes easily) should be placed on the surface when liquids are to be used. The tray serves to confine a spill.
- Good housekeeping must be practiced at all times. If an area is kept neat, clean, and free from equipment not required for the immediate procedure, the likelihood of accidental contamination or unnecessary exposure is reduced.
- Radioactive material, especially liquids, should be kept in unbreakable containers whenever possible. If glass is used, a secondary container must be provided.
- NEVER PIPETTE BY MOUTH SUCTION! Always use a mechanical pipette filling device.
- Eating, drinking, smoking, application of cosmetics, or storing of food is prohibited except in specifically defined and posted food item areas. See the Food Area Policy and Procedure in the next section for details. Food areas, including desks and tables, must be included in the monthly radiation survey.
- Refrigerators used to store radioactive material shall not be used for the storage of food. All storage compartments (refrigerator and freezer sections) must be conspicuously posted with radiation warning stickers.
- Refrigerators used for food storage must be posted as “FOOD STORAGE AREA – NO HAZARDOUS SUBSTANCES ALLOWED.” These appliances must be included in the monthly radiation survey.
- Smoking is not permitted in areas where work with unsealed radioactive sources is in progress or where contamination may exist. Under no circumstances should cigarettes, cigars, or pipes be laid on tables or benches where radioactive work has been performed or is in progress.
- Wash hands thoroughly after working with or near radioactive materials and before eating, drinking, smoking, or applying cosmetics.
- Protective gloves must be worn any time an unsealed radiation source is being used. Do not use the telephone, handle books, open cabinets, or the like with contaminated gloves. If there is a break in the skin on the hand, be sure to wear gloves.
- Lab coats and appropriate shoes must be worn by all individuals handling radioactive material.
- All reusable glassware and tools used with radioactive material should be thoroughly cleaned after use and kept separate from non-contaminated items. It is recommended that a marked container or area be provided for glassware and tools used in radioactive work.
When food areas are established in laboratories, the following rules are to be observed:
- Well-defined, fully outlined food item areas (including desks, cabinets, microwaves and refrigerators) must be established when food items are permitted in labs.
- Food item areas are to be clearly posted with a sign designating a food item area and instructing that no radioactive, chemical or infectious materials are permitted.
- Food item areas must be at least three feet from a laboratory work area or chemical storage area. In some instances, food items areas may be less than three feet if an appropriate barrier is in place, but these cases must be evaluated by EHS. In other cases, three feet may be inadequate to prevent contamination of food items, i.e., laboratory operations with a high potential for aerosolization and volatilization of chemicals or radioactive materials. Food areas are not permitted in rooms with such operations. The design of some laboratories may not allow for the designation of food areas.
- Food containers, dishes, and utensils are to be washed only in a sink exclusively designated for food utensils. Laboratory glassware or equipment are to be washed in separate sinks. Glassware or utensils that have been used for laboratory operations cannot be used for food or beverages.
- Laboratory refrigerators, ice chests, and cold rooms cannot be used for food storage. Separate equipment must be dedicated for that use and be prominently labeled.
- Designated food item areas must be free from all research-related items including personal protective equipment.
- Absolutely no chemical or radioactive materials storage is allowed above any designated food items area.
- Each individual intending to operate any radiation producing machine must be trained in its use by an individual familiar with the system.
- Each individual working with a radiation machine should know exactly what work is to be done and which applicable safety precautions should be used.
- Written operating and safety procedures must be available to personnel before operating this type of machine.
- Visitors and students in the area of work should be supervised by the equipment operator.
- Radiation producing machines must not be left unattended in an operational mode.
- Structural shielding requirements for any new installation, or any modifications to an existing unit or room, must be approved by Radiation Safety before the machine is used.
- When the safe use of the equipment depends on the mechanical set up of the unit or on technique factors, these restrictions should be closely followed.
- Under no circumstances shall shutter mechanisms or interlocks be defeated or in any way modified except in accordance with approved written procedures.
- All warning lights should be “fail safe” (specific regulations require “fail safe” features).
- A manually reset cumulative timing device should be used to indicate elapsed time and to turn off the machine when the total exposure reaches the planned amount.
- Special care is needed when working with x-ray diffraction units. Exposure rates in the primary beam can be in excess of 500,000 rems per minute at the x-ray tube (NIH, 1972). Follow the specific procedures for training, operation and emergency response that have been developed for these devices.
- Some machines such as analytical x-ray devices, irradiators and accelerators have individual safety programs. These detailed operating and emergency procedures must be posted and followed.
- Proper maintenance on all radiation producing equipment is essential. Only properly trained technical staff should perform all repairs to these instruments. Service personnel must be licensed or registered by the North Carolina Radiation Protection Section.
- Eating, drinking, smoking, and the application of cosmetics are prohibited except in areas that have been specifically designated and posted as food items areas.
- Working with radioactive materials when open wounds are present on exposed surfaces of the body is prohibited unless wounds are properly dressed and protected.
- Pipetting or any similar operation by mouth suction is prohibited.
- Protective gloves shall be worn when handling contaminated or potentially contaminated items.
- Disposable absorbent pads and remote handling devices shall be utilized when possible.
- Hands should be washed thoroughly after handling radioactive materials, especially before eating.
- Food items shall not be stored in areas designated for radioactive materials or chemicals.
- Personnel monitoring badges shall be worn in controlled areas, as applicable.
- Radioactive waste shall be disposed of only in the containers provided. Nonstandard containers are prohibited.
- Stock shipments shall be handled and stored in specially designated locations.
- Good housekeeping shall be maintained at all times.
- Spillage should be preventable, but in the event of such an accident, follow the established emergency procedures.
- Conduct radiation meter and wipe test surveys frequently. When measurements are abnormal, find the cause and correct.