Modifications in the gamma dose rate in air due to downward and lateral mobility of Cs in the soil.

Cs can be an important environmental contaminant due to fallout from nuclear reactor accidents and atomic weapons testing. Its contribution to the air gamma dose rate at 1 m height above contaminated ground depends on the soil inventory, the migration processes along the soil profile and possible modifications in the spatial distribution. In this paper the diffusion-convection equation is used to approach the Cs soil vertical migration transport and standard dose rate factors are jointly applied for estimating the air dose rate. In order to calculate the temporal reduction of the external radiation, an empirical attenuation factor is used and its coefficients are analyzed in terms of the effective diffusion coefficient and downward migration rates. Additionally, it is analyze the corrections that should be introduced in dose rate values attributable to soil redistribution processes. If these processes, natural or as a consequence of human activities, are not taken into account, both the air dose rate values and the attenuation period can be noticeably under or overestimated.