D–6
Limiting Exposure
Under average conditions, an individual working with the gauge
will receive less than 200 mrem per year.
A basic principle of radiation protection is that radiation
exposure should be kept as far below the limits as is reasonably
achievable. This is known as the ALARA (as low as reasonable
achievable) principle. The three methods for limiting exposure
are:
i Time
i Distance
i Shielding
Time
The simplest way to reduce exposure is to minimize the time
spent around a radioactive source. If the time spent near a
source is cut in half, then the exposure is halved, all other
factors remaining 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 (see Figure 15). Doubling
the distance from a radiation source reduces the exposure to
one-fourth its original value. If the distance is tripled, then the
exposure is reduced by a factor of nine, and so on.
Figure 15. Effect of Distance on Exposure
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