Sources of Radiation Exposure

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Everyone, everywhere, is exposed to radiation all the time. It is a natural part of the environment in which we live.

People are also exposed to man-made radiation, predominantly in medicine, but also from other sources. For some, radiation exposure is part of their work.


Terrestial radiation comes from the Earth: everything is naturally radioactive, including rock, soil, water, air, animals, plants, and food. The average dose from terrestial radiation is 2 mSv per year. More than half of this is from radon in your home.

Cosmic radiation comes from the Sun and outer space. The average dose from cosmic radiation is 0.4 mSv per year.

Medical procedures make up most of the man-made dose, by far. The average dose from medical diagnosis is 0.6 mSv per year.

Some people are also exposed to radiation as part of their work, from industrial uses like nuclear power plants, from accidents, and even from leftovers of atmospheric nuclear testing. On average, the dose from this is very small, about 0.01 mSv per year.

These numbers are worldwide averages. Some people are exposed to less radiation, and some more. The table to the right includes typical ranges of annual doses.

Table 1.  Annual average doses and ranges of individual doses of ionizing radiation by source (Millisieverts a )
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a Unit of measurement of effective dose.


b Globally dispersed radionuclides. The value for the nuclear fuel cycle represents the maximum per caput annual dose to the public in the future, assuming the practice continues for 100 years, and derives mainly from globally dispersed, long-lived radionuclides released during reprocessing of nuclear fuel and nuclear power plant operation.


From UNSCEAR 2008 Report Vol. I, Sources and Effects of Ionizing Radiation, Report to the General Assembly






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The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) is the leading international body on radiation levels and effects. Visit the UNSCEAR website or read the UNEP report on "Radiation Effects and Sources" based on UNSCEAR work to learn more.
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