6.1 Golden Rules

Radiation safety has two "golden rules"

Incur no unknown radiation dose.

Incur no dose not justified by benefits of the work.

Obviously, one cannot determine whether a dose is justified if the dose is not known. Determining the dose is a matter of using personnel dosimeters, survey instruments, standard calculations, and similar techniques. Proper survey techniques are necessary.

Regarding justified doses, the ALARA principle is obvious. ALARA means to keep doses As Low As Reasonably Achievable. However, ALARA is not enough; there must also be sufficient benefit derived from the actions to justify the risk. Even a very few millirem of dose is improper if no benefit will result; a dose of several rem is proper if incurred in saving life during a catastrophe.

6.2 Dose Control - External

Control of radiation doses originating outside the body usually is via control of distance, time, or shielding. Consideration of solid geometry shows that radiation intensity varies inversely as the square of the distance so long as the distance is large enough for the square to approximate a point source. For most radioisotope uses at OSU this means that the first several centimeters of distance cause a very great reduction in intensity. Hence, use of foot-long forceps, crucible tongs, pliers, etc., which keep hands at least four inches from the radioisotope vial will greatly decrease hand dose. Distances greater than a few feet have relatively little effect in most OSU situations.

Radiation dose is directly proportional to time of exposure so long as time is short compared to half-life of the radioisotope. Pre-planning work to minimize exposure time is always very prudent and sometimes a necessity.

Shielding is the most complicated of the three. For instance, primary shielding of a beta particle emitter should be plastic or other low Z material to minimize secondary x-ray production. However, secondary shielding of that same material should be lead or other high Z material for most efficient absorption of the x-rays. Neutron shielding also usually involves a combination of materials. For shielding information and assistance, ask the Radiation Safety Office.

Another dose control aspect, often ignored in the interest of obtaining low prices, is optimizing the amount of radiomaterial present. Radiomaterials not present will not cause a dose to individuals, but they also cannot produce a useful result. Do not obtain excessive quantities of radiomaterials; do not keep radiomaterial after its use has ended.

6.3 Dose Control - Internal

Minimizing doses from radioisotopes taken into the body is a matter of good work habits. The usual hygiene precautions of lab coats and gloves; not eating, smoking or licking fingers while in a radiation area; not storing food in a refrigerator containing radioisotopes, etc., will do most of what is needed. Proper use of absorbent material on work surfaces will contain the inevitable spills, reducing the spread of contamination. Direct surveys using appropriate meters and swipe surveys should be made and documented at frequent intervals to find contamination before it gets into the body. Other, more specialized techniques will be needed for some situations (hoods, glove box, etc.).