Evaluation of Radon in Soil Gas and Natural Radioactivity in Surface Soil of Kinki District, Japan

Abstract

Radon and its progeny are an important part of natural environmental exposure to radiation. However, little information is available about the radon contents of soil gas. We carried out a survey of radioactivity, focusing on 222Rn-concentrations in soil gas in parts of western Japan. Fifty nine samples in soil gas from 4 Prefectures of the Kinki district were analyzed with a liquid scintillation counter after the trapping of radon in soil gas into a toluene based-scintillation cocktail, together with 19 samples of interest from karst and uranium mining sites in another two Prefectures for comparison. The cumulative frequency of the 222Rn-concentrations in soil gas of the Kinki district showed a log-normal distribution. The average content was found to be 11.9kBqm−3 (arithmetic mean) and 7.5kBqm−3 (geometric mean). A maximum concentration of radon in soil gas, 2.1 MBqm−3 was found at the marker of the Ningyo uranium mining site. Surveys of natural radioactivity in soil were also carried out with a Ge(Li) detector to determine the concentrations in soil, mainly focusing on uranium and thorium series. The radon concentrations in soil gas were weakly correlated with those of uranium series in soils. There were no great differences vertically in the natural radioactivity in soils within 1 m, but a difference by one order of magnitude was found in soils horizontally even in the residence area of the Kinki district.