Taking advantage of all available means to limit radiation exposure
is always recommended. The three methods of limiting exposure
are:
Time
Distance
Shielding
These methods are a part of the ALARA (As Low As Reasonably
Achievable) philosophy of radiation protection.
Time
The simplest way to reduce exposure is to keep the time spent
around a radioactive source to a minimum. If time is cut in half,
then exposure is cut in half, provided all other factors remain
constant.
Distance
Distance is another effective means to reduce radiation exposure. A
formula known as the inverse square law relates the radiation
exposure rate to distance (Figure A-3). Doubling the distance from a
radiation source reduces the exposure to one-fourth its original
value. If the distance is tripled, the exposure is reduced by a factor
of nine, and so on.
Figure A-3. Effect of Distance on Exposure
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