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

摘要

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 μm, 2-63 μm and > 63 μm. ~(137)Cs 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 ~(134)Cs/~(137)Cs 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 ~(137)Cs originating from nuclear weapons, which has been in the soil for decades after fallout, and ~(137)Cs coming from the Chernobyl accident, eight years after the deposition event. This behaviour could be related to "ageing" processes of radiocaesium in soils.