Spatial distribution of natural radiation levels in Asia and its background in the earth science

This review concerns the distribution of natural radiation dose rates and/or concentrations in Asia of cosmic ray, earth crust gamma ray and radon together with its providing background and chronological fluctuation. Secondary cosmic ray yielded by the primary ray arriving at earth environment consists from ionizing components like muon and from neutron. The intensity of the ray in space varies depending on altitude and latitude and its actual data measured are presented. Earth crust gamma ray is provided by soil and rocks and derived from uranium (U-238) and thorium (Th-232) series and K-40. Data for levels of the crust gamma ray, defined as spatial absorption dose per hour at 1 m height from the outdoor earth surface (nGy/h), are present in Japan, India, China, Korea, other regions and the seabed. Half of public internal exposure dose due to natural radiation is said to be derived from Rn-222 and its daughter radionuclides yielded from Ra-226 originally. Outdoor Rn concentrations in Japan, China and Korea are presented. The causes of chronological variation are changes of solar and geomagnetic activities, supernova explosion, decay of natural radioisotopes and human activities.(K.H.)