Background Radiation - hdbk110997

DOE-HDBK-1109-97

Radiological Safety Training for Radiation-Producing (X-Ray) Devices

Student's Guide

Rem, a unit of dose equivalent, which is the energy absorbed per unit mass times the

applicable quality factor and other modifying factors.

For X-rays, it may be assumed that 1 R = 1 rad = 1 rem = 1000 mrem.

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.

DOSE LIMITS

Limits on occupational doses are based on data on the biological effects of ionizing radiation.

The International Commission on Radiological Protection and the National Council on

Radiation Protection and Measurements publish guidance for setting radiation protection

standards. The DOE, Nuclear Regulatory Commission, and Environmental Protection Agency

set regulatory requirements related to radiation protection. These limits are set to minimize the

likelihood of biological effects.