Modeling of 137Cs fixation in soils

The analysis of existing models of Cs-137 fixation in soils is presented. It is argued that the most adequate description of the experimental data is provided by the diffusion model. The main advantages of this model are the low number of parameters and the possibility to predict long-term trends in Cs-137 fixation on the basis of the results of short-term laboratory experiments. According to the diffusion model, the content of exchangeable radiocesium in different soils reaches a quasi-equilibrium state in a period from several months to several years; after this, the radiocesium mobility in the soils remains stable for a long time. However, the analysis of the main forms of stable and radioactive Cs in soils shows that there may be a second stage of Cs-137 fixation leading to a gradual decrease in its mobility with a characteristic time of several decades.