The Study On Radon Exhalation Rate From Soil

OVER the past few decades, there has been a large scientific interest in the study of environmental radon and its progenies for its associated health hazard. Many countries and regions carried out studies on mapping radon exhalation rate from soil considering the soil as the major source of environmental radon. Compared with other countries, the radon exhalation rates from common soils other than Uranium milling tails have not been well studied in our country, and the data reported on soil radon flux rate is very limited in China. While in some high background regions, the radon exhalation from soil and buiding materials made of soil causes real problems that can not be neglected.In this paper, firstly the basic knowledge on radon property, sources, hazard and protection was introduced in order to clarify the meaning of soil radon exhalation study. Then based on a systematic review of the mechanisms of radon emanation, transportation and exhalation in soil, a mathematical model for calculating radon exhalation rate from soil was established. The only input factors of the simplified model were soil radium content, dry bulk density, water content and soil texture type and the output was soil radon exhalation rate. Associated with the model, the national databases on soil radium content, soil moisture distribution and soil texture were developed so that the feasibility for mapping radon exhalation rate from soil in China was theoretically discussed. Afterwards, the principles, instruments and methods of measuring both radon exhalation rate from soil and soil properties were described in details. Field measurements of radon flux rate from soil were carried out in totally 47 points in different soil texture in Beijing, Guiyang and Huhhot. The averages and ranges in the three cities were 13.2 (3.1~49.9), 34.8 (4.6~128.5)和14.0 (2.0~29.0)mBq/m2s. Then based on both the theories and the measurement data on radon flux rate and soil properties, the influences of soil radium content, moisture saturation, soil porosity and soil texture were analyzed. And the above theoretical model was validated and modified using the field measurement data. We also introduced our practical measurements on radon flux rate and indoor concentration in Yangjiang city of Guangdong province with high radiation background by use of ERS-2 instrument which indicated the significance of the study on radon exhalation from both environmental soil and indoor buiding materials.