Depth migration of chernobyl originated 137Cs and 90Sr in soils of Belarus

Depth migration of 137Cs and 90Sr was studied in soils of reference sites that have different environmental characteristics and are situated in all four radiogeochemical regions of Belarus. The parameters as used were: the fraction of the nuclide inventory below a depth of 2 cm; the fraction of the nuclide inventory below a depth of 5 cm; and the thickness of the top soil layer containing 90% of the nuclide inventory. Despite the apparent differences in the nuclide migration at various sites, some common tendencies were observed. During the first 3–5 years after the accident, the 90Sr depth migration at several watershed and terrace sites did not exceed that of 137Cs. About 5–15% of the nuclide inventories are below the depth of 5 cm, and 90% are contained in the top 3–7 cm soil layer. However, at the floodplain reference sites, a pronounced tendency for a higher migration rate of 90Sr was revealed. Less than 5% of the 137Cs inventory but about 5–30% of the 90Sr inventory are below 5 cm, and the top soil layer containing 90% of the nuclide inventory is 1–2 cm thicker for 90Sr.