Examination of the effect of particle size on the radionuclide content of soils

Information on the distribution of radiocaesium as a function of soil particle size is fundamental for its use as tracer in soil transport. Since the processes involved in soil erosion are known to remove and transport finer particles with larger efficiency, the aim of this work was to obtain data on the particle size versus radionuclide content distribution regarding the reference site of a soil erosion study. The analysis done was based on more than 5 kg of source material and the changes happened to the radionuclide content of the different size fractions between the individual separation steps have been carefully monitored. About 10% of the total amount of 137Cs present was found to be trapped in the serrations of larger stone-fragments while another 10% is transportable only during heavier storm-events. Within the remaining 80%, physical weathering products and clay particles have a 137Cs-activity concentration, transportability and mass ratio of about 1:10, 1:2 and 1:1, respectively.