Natural radioactivity

Background radiation is the ionizing radiation present in the environment. Background radiation originates from a variety of sources, both natural and artificial. Sources include cosmic radiation, naturally occurring radioactive materials such as radon, and fallout from nuclear weapons testing and nuclear accidents.

The term background radiation can have different meanings, depending whether we are considering an ambient radiation dose, or we wish to differentiate between an incidental background and a particular source of radiation of concern.

For example, in considering radiation safety , background radiation is defined by the International Atomic Energy Agency as "Dose or dose rate (or an observed measure related to the dose or dose rate) attributable to all sources other than the one(s) specified. So a distinction is made between sources of dose which are incidentally in a location, which are defined here as being "background", and the dose due to a specified source. This is important where radiation measurements are taken of a specified radiation source, and the incidental background may affect this measurement. An example would be detection of radioactive contamination in a gamma ray background, which could increase the total reading above that expected from the contamination alone.

However, if no specific radiation source is of concern, then the total radiation dose measurement taken at a location is generally called the background radiation , and this is usually the case where an ambient dose rate is measured for environmental purposes.

Background radiation varies with location and time, and the following table gives examples:

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.

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