Low-Level Radiation

What It Is and Where It Occurs

Naturally occurring forms of radiation are part of “background radiation,” which people are continually exposed to in varying degrees. Naturally occurring forms account for an average of 82% of the exposures in the U.S. population, according to the National Council on Radiation Protection and Measurements (NCRP). These exposures come from a variety of sources, such as cosmic radiation from outer space and internal emissions from radioactive materials ingested in food and water and from the body itself. Exposures also occur from radioactive minerals in soils and rocks. By far, the largest background exposure (52%) comes from radon, a colorless, odorless radioactive gas that originates from uranium in the soil, which can seep into people's houses in air and water. In high enough concentrations, radioactive particles from radon can damage cells that line the lungs and lead to lung cancer. Radon is the second leading cause of lung cancer in the United States and is associated with 15,000 to 22,000 lung cancer deaths each year, according to the National Cancer Institute.

Human-made low-level radiation accounts for about 18% of the total background exposure, [Page 451]according to the NRCP, with medical X-rays and nuclear medicine making up the majority of this human-made exposure in the United States. Other exposures can come from building materials, such as the granite in Grand Central Station in New York and consumer products such as computer screens, smoke detectors, and tobacco. Low levels of radiation also are emitted from nuclear plants and nuclear weapons facilities and from widespread fallout from aboveground testing of nuclear weapons that occurred in the United States from 1951 to 1962. However, for most people, these sources account for only a small portion of human-made background exposure, according to the NCRP.

Unless they live near or work at a nuclear power or nuclear weapons plant or have radon in their homes, the majority of people are most frequently exposed to low levels of radiation through medical and dental X-rays and diagnostic tests.

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