Mathematical model of 137Cs migration in soil: analysis of observations following the Chernobyl accident

The applicability of traditional mathematical models is studied on the basis of 3 y of observation of the vertical migration of 137Cs fallout after the Chernobyl accident. The most accurate description of the dependence of the radionuclide concentration on the depth of the soil layer is given by a lognormal distribution. The parameters of this distribution are determined and shown to be a solution to the Fokker-Planck equation, a special case of which is the diffusion-convection transport equation.