Preliminary Study on a Regional Radon Concentration in Surface Soil Prediction Method

Abstract

A reformulated mathematical equation for predicting radon concentration in surface soil has been established based on the diffusive and convection theory. The parameters in the equation, such as radon emanation coefficient, convection velocity, diffusion coefficient, porosity of soil and so on, are closely related to the soil types. In order to determine these parameters, field measurement were carried out in totally 31 sites covering four types of soil in Chengdu Area, China. And least squares fitting algorithm and inversion fitting computation were also used. The prediction equation is ultimately applied to map the radon concentration in surface soil of Chengdu Area along with the geochemical databases of uranium content distribution in soil and soil texture distribution. According to the field measurement results on 17 sites in Chengdu, the prediction was verified to work property. About 50% of the natural radiation dose which people accepted is contributed from radon and its short-life progenies. And more and more attentions are paid on the issue of the health risks from them. In fact, radon in the ambient air is mainly released from the radioactive elements uranium and radium in the soil and rocks underground. Therefore, it is of significance for radon control to delineate the potential high radon zone combining the local geological background. Especially in China, the environmental radon survey started relatively late. A large-scale indoor radon measurement has not been conducted yet. However, the database based on regional geological survey has been built in many localities. A great number of geochemical data such as the uranium content and the distribution of soil texture are available. It is a feasible way to predict the regional radon distribution quickly and efficiently by combining these data with radon migration theory. Based on a steady-state radon transport model in porous materials 1) , combined with the local geological and pedological parameters, several methodologies were also developed for predicting a regional radon concentration 2-4) . In this paper, a methodology for predicting the radon distribution in surface soil of Chengdu Area was introduced. First, a reformulated simplified mathematical equation for the prediction was established by using a new boundary condition, i.e., the flux density of radon on ground-air interface is continuous and equal. Second, the parameters in the radon concentration equation, such as radium content, soil porosity and so on, were measured by field samples. The theoretical radon value was calculated and compared with the measured value. The ultimate prediction equation was derived by corrected and verified by field measured results.