Using soil cesium migration models to predict human external exposure

Based on existing analytical models of ¹³⁷Cs migration and data on the vertical distribution of ¹³⁷Cs in soils in areas contaminated as a result of the Chernobyl accident, a forecast of the dose rate of gamma radiation in the air has been developed. To estimate the radionuclide distribution in the soil, solutions of the convective-diffusion equation and the log-normal distribution were used. As the best fit to the real distributions of ¹³⁷Cs radionuclide in soil was found the chi-squared distribution which is a solution of the convective-diffusion equation with an increasing dispersion coefficient and the log-normal distribution. For both distributions, the dependence of the parameters (dispersion coefficient and velocity of directed movement with soil moisture) on time was found. Based on the assumption of the universality of these dependences, a new method for their reconstruction in time is proposed using a once-selected profile of global fallout. The absorbed dose rates in the air for Russian regions Kola Peninsula and Arkhangelsk Oblast was calculated up to 50 years after the fallout.