Table 16.6 - Worldwide annual average effective dose to adults from natural sources of ionising radiation

Source: UNSCEAR, 1993

Component of exposure Annual effective dose (mSv)
In areas of normal background In areas of elevated exposures
Cosmic rays 0.38 2.0
Cosmogenic radionuclides 0.01 0.01
Terrestrial radiation: external exposure 0.46 4.3
Terrestrial radiation: internal exposure (excluding radon) 0.23 0.6
Terrestrial radiation: internal exposure from radon
and its decay products:
inhalation of Rn-222 1.2 10
inhalation of Rn-220 0.07 0.1
ingestion of Rn-222 0.005 0.1
Total 2.4 ­

Note: Other sources not included in the worldwide averages include: the increase in cosmic radiation exposure during air travel, the exposure of radiological workers, exposure due to the Chernobyl accident and fall-out from nuclear weapons testing. Radiation doses are expressed in sieverts (Sv), which are a measure of the amount of energy absorbed by unit mass of tissue (see Effects and risks in the text).