Distribution of pre- and post-Chernobyl radiocaesium with particle size fractions of soils

The association of radiocaesium with particle size fractions separated by sieving and settling from soils sampled eight years after the Chernobyl accident has been determined. The three size fractions were: < 2 mu m, 2-63 mu m and > 63 mu m. Cs-137 in the soil samples was associated essentially with the finer size fractions, which generally showed specific activities 3-5 times higher than the bulk samples. Activity ratios of Cs-134/Cs-137 in the clay-sized fractions appear to be lower with respect to the corresponding values in bulk soil samples. This result indicates that some differences still exists in the particle size distribution between Cs-137 originating from nuclear weapons, which has been in the soil for decades after fallout, and Cs-137 coming from the Chernobyl accident, eight years after the deposition event. This behaviour could be related to ageing processes of radiocaesium in soils. (c) 2005 Elsevier Ltd. All rights reserved.