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ICRPAEDIA: Sources of Radiation


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 inclues typical ranges of annual doses.

Table 1.  Annual average doses and ranges of individual doses of ionizing radiation by source (Millisievertsa)

Source or mode Annual average dose (worldwide) Typical range of individual doses Comments
Natural sources of exposure
Inhalation (radon gas) 1.26 0.2–10 The dose is much higher in some dwellings.
External terrestrial 0.48 0.3–1 The dose is higher in some locations.
Ingestion 0.29 0.2–1  
Cosmic radiation 0.39 0.3–1 The dose increases with altitude.
Total natural 2.4 1–13 Sizeable population groups receive 10-20 millisieverts (mSv).
Artificial sources of exposure
Medical diagnosis (not therapy) 0.6 0-several tens The averages for different levels of health care range from 0.03 to 2.0 mSv; averages for some countries are higher than that due to natural sources; individual doses depend on specific examinations.
Atmospheric nuclear testing 0.005 Some higher doses around test sites still occur. The average has fallen from a peak of 0.11 mSv in 1963.
Occupational exposure 0.005 ~0–20 The average dose to all workers is 0.7 mSv. Most of the average dose and most high exposures are due to natural radiation (specifically radon in mines).
Chernobyl accident 0.002b In 1986, the average dose to more than 300,000 recovery workers was nearly 150 mSv; and more than 350,000 other individuals received doses greater than 10 mSv. The average in the northern hemisphere has decreased from a maximum of 0.04 mSv in 1986. Thyroid doses were much higher.
Nuclear fuel cycle (public exposure) 0.002b Doses are up to 0.02 mSv for critical groups at 1 km from some nuclear reactor sites.  
Total artificial 0.6 From essentially zero to several tens Individual doses depend primarily on medical treatment, occupational exposure and proximity to test or accident sites.

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

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.