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Health Effects
Understanding Radiation:  

Radiation Doses in Perspective

Health Effects

A dose is the amount of radiation energy absorbed by the body. The United States unit of measurement for radiation dose is the rem (Roentgen Equivalent Man). In the U.S., doses are most commonly reported in millirem (mrem). A millirem is one thousandth of a rem (1000 mrem = 1 rem).

Most other countries  measure radiation dose using the metric system unit of Sieverts (Sv). A milliSievert is one thousandth of a Sievert (1000 mSv = 1 Sv). Converting Sieverts to rems is easy. One sievert equals 100 rem (1 Sv = 100 rem). One milliSievert equals one hundred millrems (1 mSv = 100 millrems).

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Average U.S. Radiation Doses and Sources

All of us are exposed to radiation every day, both from natural sources such minerals in the ground and from man-made sources such as medical x-rays. According to the National Council on Radiation Protection and Measurement, the average annual radiation dose per person in the U.S. is 620 millirem (6.2 milliSieverts). The pie chart below shows the sources of this average dose.

Sources of Radiation Exposure Pie Chart

Figure reprinted with permission of the National Council on Radiation Protection and Measurements. Exit EPA Disclaimer

Half of our average dose comes from natural background sources: cosmic radiation from space, naturally occurring radioactive minerals in the ground and in your body, and from the radioactive gasses radon and thoron, which are created when other naturally occurring elements undergo radioactive decay. Another 48 percent of our dose comes from medical diagnostics and treatments.

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Doses from Common Radiation Sources

The following diagram compares radiation doses from common radiation sources, both natural and man-made.

Relative Doses from Radiation Sources

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