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|  DOE-HDBK-1109-97
Radiological Safety Training for Radiation-Producing (X-Ray) Devices
Instructor's Guide
Lesson Plan
Instructor's Notes
For X-rays, it may be assumed that 1 R = 1 rad = 1 rem
= 1000 mrem.
F.
BACKGROUND RADIATION
Background radiation, to which everyone is exposed,
comes from both natural and manmade sources.
Natural background radiation can be categorized as
cosmic and terrestrial. Radon is the major contributor
to terrestrial background. The most common sources of
manmade background radiation are medical procedures
and consumer products.
The average background dose to the general population
from both natural and manmade sources is about 350
mrem per year to the whole body. Naturally occurring
sources contribute an average of 200 mrem per year
from radon daughters, about 40 mrem per year from
internal emitters such as potassium-40, about 30 mrem
per year from cosmic and cosmogenic sources, and
about 30 mrem per year from terrestrial sources such as
naturally occurring uranium and thorium. Manmade
sources contribute an average of about 50 mrem per
year to the whole body from medical procedures such as
chest X-rays.
The deep dose equivalent from a chest X-ray is 5 - 10
mrem, a dental X-ray is 50 - 300 mrem, and
mammography is 0.5 - 2 rem.
10
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