Describing the observed vertical transport of radiocesium in specific soils with three time-dependent models.

In this paper three transport models are applied to describe the vertical migration process of 137Cs in undisturbed soil. The same experimental data set is used for the calibration of each model. These data were obtained from areas in northeast Italy, where the 137Cs deposition following the Chernobyl accident ranged from 20 to 40 kBq m-2. A diffusion model (called DSF) is presented, which takes into account three states of cesium in the soil matrix: mobile, sorbed and bound. It is shown that this model provides a reasonably good description of the temporal evolution of the radiocesium profile in soil. In addition, a new version of the RABES model (called RABES I) is proposed, with only two free parameters: the rate of change of the vertical profile and the diffusion length in the equilibrium. This paper includes a critical evaluation among the DSF, RABES and RABES I models, considering, mainly, their predictive aspect about the temporal change of the radiocesium profile in soil.