Finite element modeling of radon distribution in natural soils of different geophysical regions

Abstract

Abstract Radon migration from deep soil to the earth’s surface is investigated numerically using a developed Finite Element numerical model. The objectives of this study are: to predict the radon profile variation with the soil depth, the radon diffusion coefficients in multi-layer soils, the surface radon concentrations, and the soil–air radon fluxes. The flexibility of the Finite Element Method allows for accommodating varying diffusion coefficients in multi-layer soils and expressing convective-type boundary conditions. The convective-type boundary condition assumes that the surface radon flux is proportional to the difference between the radon concentration in the ambient air and the radon concentration at the soil surface. Radon concentration profiles with depth were collected from several geophysical locations such as Greece, Germany, South Africa, and Jordan. The numerical results show that the multi-layer profile of radon in natural soils is more descriptive than the one-layer one used traditionally, where each layer has its own diffusion coefficient. The effective diffusion coefficient, D, shows variation with the soil depth and its value differs from one geophysical location to another. A constant soil–air interface transfer coefficient is calculated and the soil–air radon flux is accordingly estimated. In addition, the surface radon concentrations at the soil–air interface are calculated from the model and compared against extrapolated field data.