<P> 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 . </P> <P> Background radiation varies with location and time, and the following table gives examples: </P> <Table> Average annual human exposure to ionizing radiation in millisieverts (mSv) per year <Tr> <Th> Radiation source </Th> <Th> World </Th> <Th> US </Th> <Th> Japan </Th> <Th> Remark </Th> </Tr> <Tr> <Td> Inhalation of air </Td> <Td> 1.26 </Td> <Td> 2.28 </Td> <Td> 0.40 </Td> <Td> mainly from radon, depends on indoor accumulation </Td> </Tr> <Tr> <Td> Ingestion of food & water </Td> <Td> 0.29 </Td> <Td> 0.28 </Td> <Td> 0.40 </Td> <Td> (K - 40, C - 14, etc .) </Td> </Tr> <Tr> <Td> Terrestrial radiation from ground </Td> <Td> 0.48 </Td> <Td> 0.21 </Td> <Td> 0.40 </Td> <Td> depends on soil and building material </Td> </Tr> <Tr> <Td> Cosmic radiation from space </Td> <Td> 0.39 </Td> <Td> 0.33 </Td> <Td> 0.30 </Td> <Td> depends on altitude </Td> </Tr> <Tr> <Td> sub total (natural) </Td> <Td> 2.40 </Td> <Td> 3.10 </Td> <Td> 1.50 </Td> <Td> sizeable population groups receive 10--20 mSv </Td> </Tr> <Tr> <Td> Medical </Td> <Td> 0.60 </Td> <Td> 3.00 </Td> <Td> 2.30 </Td> <Td> worldwide figure excludes radiotherapy; US figure is mostly CT scans and nuclear medicine . </Td> </Tr> <Tr> <Td> Consumer items </Td> <Td>--</Td> <Td> 0.13 </Td> <Td> </Td> <Td> cigarettes, air travel, building materials, etc . </Td> </Tr> <Tr> <Td> Atmospheric nuclear testing </Td> <Td> 0.005 </Td> <Td>--</Td> <Td> 0.01 </Td> <Td> peak of 0.11 mSv in 1963 and declining since; higher near sites </Td> </Tr> <Tr> <Td> Occupational exposure </Td> <Td> 0.005 </Td> <Td> 0.005 </Td> <Td> 0.01 </Td> <Td> worldwide average to workers only is 0.7 mSv, mostly due to radon in mines; US is mostly due to medical and aviation workers . </Td> </Tr> <Tr> <Td> Chernobyl accident </Td> <Td> 0.002 </Td> <Td>--</Td> <Td> 0.01 </Td> <Td> peak of 0.04 mSv in 1986 and declining since; higher near site </Td> </Tr> <Tr> <Td> Nuclear fuel cycle </Td> <Td> 0.0002 </Td> <Td> </Td> <Td> 0.001 </Td> <Td> up to 0.02 mSv near sites; excludes occupational exposure </Td> </Tr> <Tr> <Td> Other </Td> <Td>--</Td> <Td> 0.003 </Td> <Td> </Td> <Td> Industrial, security, medical, educational, and research </Td> </Tr> <Tr> <Td> sub total (artificial) </Td> <Td> 0.61 </Td> <Td> 3.14 </Td> <Td> 2.33 </Td> <Td> </Td> </Tr> <Tr> <Td> Total </Td> <Td> 3.01 </Td> <Td> 6.24 </Td> <Td> 3.83 </Td> <Td> millisieverts per year </Td> </Tr> </Table> <Tr> <Th> Radiation source </Th> <Th> World </Th> <Th> US </Th> <Th> Japan </Th> <Th> Remark </Th> </Tr>

What is the average annual dose of radiation