Evaluation of Natural Radioactivity in Subsurface Air, Water and Soil in Western Japan

Surveys of radon concentrations in western Japan were carried out to estimate the contents not only of waters in the environment but also in soil gas. The maximum concentration measured for drinking water as public supply exceeded the 1991 United States Environmental Protection Agency-recommended limit for drinking water (11 Bq L-1) but did not exceed that of several European countries (100 Bq L-1). Overall, the concentrations of radon in subsurface water ranged from 1 to 100 Bq L-1 and those in surface water were below 1 Bq L-1 in a residential area. Fifty nine samples in soil gas at 4 Prefectures of the Kinki district were analyzed together with 19 samples of interest due to karst and uranium mining sites from another two Prefectures to compare with the above samples. The cumulative frequency of the Rn-222-concentrations both in environmental water and soil gas showed a log-normal distribution. Surveys of natural radioactivity in soils were also carried out with a Ge(Li) detector to determine the concentrations.