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An investigation of radon exhalation rate from soil by using a 'closed-can' method with activated charcoal absorption has been carried out on a large scale to determine radon exhalation rate of about 144 samples covering sedimentary and granite areas in Beijing, Zhuhai, Qinhuangdao and Shijiazhuang cities in China. The average of radon exhalation rate in sedimentary area is 20.71±3.45 mBq.m-2 s-1, and 72.51±62.16 mBq.m-2 s-1 in granite area (not including abnormal sites). The maximum observed exhalation rate is 620.76 mBq.m-2 s-1 in Zhuhai area. There are small exhalation rate differences in sedimentary areas, but obvious differences between different sites in granite areas. Season variation of radon exhalation rate is not notable but it was influenced by moisture content and porosity of soil in sedimentary area. It was found that calculated radon exhalation rates were not consistent with measured values. The calculated values were lower than measured ones in sedimentary areas but no definite correlation in granite areas. Different geologic terrains of the southern China indicate some of the problems inherent by correlating radon exhalation rate with geology. More detailed and larger scale investigation should be conducted for mapping nationwide radon exhalation rate from soil in China.
KEYWORDS: radon exhalation rate, activated charcoal absorption, mapping, China
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