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Background radiation
Background radiation is the ubiquitous ionizing radiation that people on the planet Earth are exposed to, including natural and artificial sources.
Both natural and artificial background radiation varies depending on location and altitude.
==Natural background radiation==
Radioactive material is found throughout nature. Detectable amounts occur naturally in soil, rocks, water, air, and vegetation, from which it is inhaled and ingested into the body. In addition to this ''internal exposure'', humans also receive ''external exposure'' from radioactive materials that remain outside the body and from cosmic radiation from space. The worldwide average natural dose to humans is about 2.4 millisievert (mSv) per year.〔 This is four times the worldwide average artificial radiation exposure, which in 2008 amounted to about 0.6 mSv per year. In some rich countries, like the US and Japan, artificial exposure is, on average, greater than the natural exposure, due to greater access to medical imaging. In Europe, average natural background exposure by country ranges from under 2 mSv annually in the United Kingdom to more than 7 mSv annually for some groups of people in Finland.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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