Level of Radon Exhalation Rate from Soil in Some Sedimentary and Granite Areas in China

An investigation of radon exhalation rate from soil by using a 'closed-can' method with activated charcoal absorption on a small scale has been carried out to determine the radon exhalation rate of about 144 samples from sedimentary and granite areas in the urban areas of Beijing, Zhuhai, Qinhuangdao, and Shijiazhuang in China. The average radon exhalation rates are 20.71 ± 3:45 mBq.m −2 .s −1 in the sedimentary areas and 72.51 ± 62.16 mBq.m −2 .s −1 in the granite areas except abnormal sites. The observed maximum exhalation rate is 620.76 mBq.m −2 .s −1 in the Zhuhai area. A small difference in radon exhalation rate was observed in the sedimentary areas, but a large difference was observed in the granite areas. Radon exhalation rate is obviously influenced by moisture content and porosity of soil. It is found that calculated radon exhalation rates are not consistent with measured values. The calculated values are lower than measured ones in the sedimentary areas but no definite correlation between them exists in the granite areas. Different geologic terrains in southern China lead to inherent problems determined by correlating radon exhalation rate with geological setting. Investigation on a larger scale and in greater detail should be conducted for mapping nationwide radon exhalation rate from soil in China.