Occupational exposure limits are set by government agencies.
The current limit in the United States and many other countries
is 5,000 millirem per year. Under average conditions, a full time
employee working with the 3241 will receive less than 200
millirem per year.
Anyone working with or near radioactive materials is subject to
the limits on occupational exposure mentioned earlier and must
complete a radiation safety training course to be designated an
authorized user. As an authorized user, an individual so
designated must work in a “controlled” environment to the
extent that their exposure to radiation must be monitored.
Several means of personnel monitoring or dosimetry exist; the
most common methods are film badges and TLD badges, available
from Troxler.
Radiation Statistics
Radioactive emission is a random process. The number of
emissions in a given time period is not constant but varies
statistically about an average value. The variation about the true
mean value is a Poisson distribution. In this distribution, the
standard deviation () about the mean (n) is defined as:
= n.
When the mean is greater than 100, the Poisson distribution can
be closely approximated by the normal distribution (Figure 12).
The normal distribution predicts the probability that any given
count rate will fall within a selected region about the mean.
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