Model 3440-L C–3
RADIATION EXPOSURE
Government agencies set occupational exposure limits. The current limit in
the United States and in many other countries is 5,000 mrem per year.
Under average conditions, a full time employee working with the 3440-L
gauge will receive less than 200 mrem per year.
Taking advantage of all available means to limit radiation exposure is
always recommended. The three methods of limiting exposure are:
TIME
DISTANCE
C. RADIOLOGICAL SAFET
SHIELDING
These methods are a part of the ALARA (As Low As Reasonably
Achievable) concept.
The simplest way to reduce exposure is to keep the time spent around
radioactive source to a minimum. If time is cut in half, so is the exposure,
with all other factors remaining constant.
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 C–1). 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, etc.
Figure C–1. Effect of Distance on Exposure
Shielding is any material used to reduce the radiation reaching the operator
from a radioactive source. While some types of radiation such as alpha
particles may be stopped by a single sheet of paper, other radiation such as
photons and neutrons require much more shielding. Dense materials, such
as lead, shield photons. Materials containing large amounts of hydrogen,
such as polyethylene, shield neutrons. The Model 3440-L has built-in
shielding to reduce the exposure.
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