Methodology study on evaluation of radon flux from soil in China.

Radon flux rate from soil is one of the most important factors for the evaluation of environmental radon levels. The objective of our study is to make a rough estimation of the nationwide radon flux rate from soil in China. Considering the applicability to the large area and complex distribution of soil types in China, a simple model was established. To test the model, field measurements on radon flux rate totally in 47 points from different areas were carried out from spring to summer in 2003. Laboratory experiments of each soil sample on related soil properties, such as radium contents, water contents, soil dry bulk density and soil texture were performed simultaneously. Approximately 30% of the samples had very consistent calculated values with their measured values, their relative errors were less than 0.25. In spite of the large uncertainties in the model which is influenced by so many factors, the considerable validation of the model can be shown. Based on the discussion of distribution of the errors as well as the reasons causing the errors, a trial modification of the model was made. A modification function looked necessary when soil water content was <10%.