SECTION IV

BASIC RADIATION PROTECTION PRINCIPLES

A. RADIATION PROTECTION STANDARDS

TEDE = TOTAL EFFECTIVE DOSE EQUIVALENT
SDE  = SHALLOW DOSE EQUIVALENT
LDE  = LENS OF EYE DOSE EQUIVALENT

ALARA PHILOSOPHY

Current scientific evidence concedes that there may not be a risk-free level of radiation exposure.  Therefore, in addition to providing an upper limit on a person's permissible radiation exposure, the NRC also requires that its licensees maintain occupational exposures as low as reasonably achievable (ALARA).  This means that every activity involving exposure to radiation should be planned so as to minimize unnecessary exposure to individual workers and the worker population.  All experimental procedures should be reviewed with the objective of reducing unnecessary exposures.

An ALARA program has been incorporated as part of the University’s NRC license.  It outlines the responsibilities of several groups.  Management has the responsibility to provide an administrative organization and the resources to operate it.  The University Radiation Safety Committee must review occupational radiation exposures.  The Radiation Safety Officer ensures that training is given, will review authorized users’ procedures and physical layouts, and will investigate radiation exposures that exceed ten percent of the annual limit.  The Authorized User will ensure that laboratory personnel are properly trained and will consult with the RSO with regard to keeping exposures ALARA.  The radiation worker will consider ALARA when conducting research in the laboratory and will consult with the Authorized User or the Radiation Safety Office when safety or other laboratory practices are in question.

The University of Pittsburgh has set an ALARA action level at 10 percent of the annual Federal and State radiation exposure limits.  Annual cumulative radiation exposures are reviewed each calendar quarter.  Action levels are at 10%, 30% and 80% of the annual allowable dose. If it is determined through monitoring or calculation that any worker has exceeded 30 percent of the applicable radiation exposure limits, an investigation will be conducted to determine the cause of the exposure and to develop methods to control future exposures.  A summary of exposure for any individuals exceeding these levels is presented to the University Radiation Safety Committee at it’s next quarterly meeting. 

B. EXTERNAL RADIATION PROTECTION PRINCIPLES

TIME

Radiation doses are directly proportional to the exposure time in the field.  If the time spent in a given radiation field is doubled, the worker's dose is doubled.  Therefore, to limit radiation doses, the time spent in the field must be limited.

Radiation Dose (Time in field)  

DISTANCE

The radiation dose received from a source is inversely proportional to the square of the distance of separation.  If the distance is increased ten-fold the exposure will be cut down to one percent.  Thus, the distance of separation between a person and a "point" source has a relatively greater influence on dose than the time factor.

Radiation dose 1 / (Distance of Separation)²  

SHIELDING

Any substance may serve to attenuate radiation to acceptable levels provided sufficient thickness is used.  Certain materials, however, are more effective in shielding certain types of radiation.

Alpha particles are stopped by an ordinary sheet of paper or a few inches of air.

Beta particles although more penetrating than alpha, can be absorbed readily and completely.  Figure 4 shows the shielding required for complete absorption of beta rays of various energies in various substances.  For example, beta rays of one million electron volts (MeV) are completely absorbed by 0.15 cm of aluminum.

Radiation Health Handbook (Range in air. Range in plastic x 1000)

Gamma rays and x-rays of a single energy (monoenergetic) are attenuated exponentially;  therefore, theoretically it is not possible to attenuate the radiation completely, although the exposure rate can be reduced by any desired factor.  Thus, if a certain thickness of absorber, the half-value layer (HVL), reduces the dose to one-half the initial amount, then a thickness of three such layers will reduce the dose to one-eighth (½ x ½ x ½) the initial amount.  Similarly three tenth-value layers (TVL) will reduce the dose to 1/1000 of the initial amount (1/10 x 1/10 x 1/10).  Shielding materials of high density and high atomic number, such as lead, are generally the most effective absorbers or shields for x- and gamma rays.  Thus, less thickness and weight per square foot is required for such materials.  However, steel, concrete, brick, or other materials can provide the same degree of protection if used in appropriately greater thicknesses.

C. INTERNAL RADIATION PROTECTION PRINCIPLES

An internal radiation hazard exists when radionuclides can enter the body by ingestion or inhalation, through wounds, or by direct absorption through intact skin.  The radiation doses are often difficult to evaluate and depend on many factors such as the physical and chemical form of the material, the mode of entry, and the individual's metabolism.  A certain quantity of radioactive material within the body represents a greater hazard than the same activity as an external source because the tissue is irradiated continuously until the material has decayed or been eliminated.  Even weakly penetrating radiations such as low-energy beta particles present a hazard since all their energy will be dissipated in the tissue.  

The principal means of protection from internal radiation is containment of the radioactive source.  Control measures must be taken to prevent the contamination of working surfaces, equipment, and personnel.  The following covers some of these safety precautions and procedures.

D. GENERAL PRECAUTIONS AND SAFETY PROCEDURES WHEN WORKING WITH RADIOACTIVE MATERIALS

1. Be familiar with the particular clinical or experimental procedure being performed.  Never perform extensive radiochemical work with hazardous levels of material until the procedure has been tested by a "dry run" to preclude unexpected complications.
   

2. Keep radioactive and non-radioactive work separate as much as possible by maintaining designated and labeled areas on the bench top and in the laboratory.
   

3. Cover work surfaces with absorbent padding that has a plastic backing to protect furniture and facilitate clean up.  Use stainless steel or plastic trays to help control liquids if these are spilled.
   

4. When working with radioactive materials, wear a laboratory coat and plastic or rubber gloves for protection of clothes and skin.  To avoid the spread of contamination, remove gloves at the work area.  Change gloves frequently to prevent the spread of contamination.  Do not handle faucets, light switches, door knobs, telephones, etc., with contaminated gloves.  Special protection may be required for open cuts or wounds.
   

5. Monitor yourself for contamination at frequent intervals when working with radioactive materials.  Monitoring should include hands, body, shoes, and protective clothing.
   

6. Clean up after yourself.  Do not leave the laboratory contaminated or in a mess.  Check all work areas for contamination.  Before leaving the laboratory, wash your hands thoroughly.
   

7. Never pipette radioactive solutions by mouth.  Mechanical devices must be used.  Push-button pipetters with disposable tips are strongly recommended.

8. 
   To prevent accidental ingestion of radioactive materials, do not eat, drink, smoke, store or prepare food, or apply cosmetics in restricted areas.
   

9. Do not handle sources of high radioactivity directly with your fingers.  Use tongs.
   

10. Observe time, distance, shielding, and contamination control while working with radioactive materials or while in a radiation area.
    

11. If you are designated to wear a personnel (TLD) monitoring badge, you should wear it at all times when working with or near radioactive materials for which the badge is appropriate.
    

12. Have containers for radioactive waste and contaminated glassware at the work location.  Avoid transporting contaminated articles from the work area through clean laboratory areas.  Shield the waste containers as required to prevent unnecessary exposure.
    

13. Confine work with gaseous, volatile, or dust-forming radioactive material to fume hoods or glove boxes, if appropriate.
    

14. Label containers of radioactive material clearly, indicating radionuclide, activity, compound, date, and radiation level, if applicable.

E. EMERGENCY PROCEDURES

In case of a spill of radioactive material, the following procedures should be performed: 

1. Alert others in the laboratory that a spill has occurred.
   

2. Contain and minimize the spread of contamination by covering the spill with absorbent material such as paper towels, padding, Kimwipes, etc.  Cordon off the suspected area of contamination, or seal off the laboratory if the radioactive material is of a volatile nature.
   

3. Contact the Radiation Safety Office as soon as possible.
   

4. Taking the necessary precautions to limit exposure, determine the extent of contamination by monitoring the area with the appropriate survey instrument and/or by performing a smear survey.
   

5. To clean up the spill:  Decontaminate the area in convenient sectors by starting from the outer edge with a wiping and scrubbing motion and working in towards the center.  Use a commercial decontamination product or a soap and water cleaning solution on paper towels or pads.  Other additives such as alcohol or EDTA may also be used, depending on the chemical form of the contamination.  Sodium bicarbonate should be used with radioiodine spills to buffer the pH and reduce the volatilization of iodine gas.
   

6. Package the contaminated waste from the clean-up in a yellow bag and  re-survey the area to make sure that there is no residual contamination.
   

7. The Radiation Safety Office will assist in the monitoring, clean up, and survey operations.    

In case of personnel contamination, the following procedures should be performed:

1. Immediately remove any contaminated clothing or shoes, exercising caution not to spread or track the contamination further.
   

2. Wash contaminated areas of skin with soap and water.  Do not use hot water and do not use abrasive scrubbing, as this will only increase the passage of radioactive material through the skin.
   

3. Call the Radiation Safety Office to evaluate the exposure. (412-624-2728)

Section V
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