Caesium-137 migration in Hungarian soils.

Distribution of 137Cs activity concentration has been measured in soils from 19 Hungarian counties. The levels of soil contamination in Hungary after the Chernobyl fallout are sufficient to study the vertical distribution of the 137Cs under natural conditions. Samples were taken layer by layer on plain, grassy and uncultivated fields down to a depth of 20 cm. The results show that radiocaesium migrates very slowly in the soils investigated. The 137Cs concentration peaks in almost all of the soils remain in the top 5 cm layer, but the distribution patterns are different. Variations in diffusion, sorption-desorption, and complexing processes, plant uptake and plant- and animal-originated mechanical changes result in the formation of site-specific radionuclide distribution profiles. On the basis of the experimental data a model has been developed for the long-term prediction of the 137Cs migration. By application of an applied diffusion-convection model the results can be well fitted, the initial deposition can be calculated and the data can be used for the long-term prediction of the 137Cs distribution profile.