Characterisation of Chernobyl fallout in Belarus soil
Soil samples originating from the Chernobyl Exclusion Zone and Vetka region of Southern Belarus, which are contaminated by radioactive Chernobyl fallout were analysed using three analytical procedures which were developed for this work: 1. A Differential Autoradiographic Imaging (DAI) procedure which allows the non destructive isotopic classification of radioactive contamination in soil. This technique enabled differentiation of certain isotopes, including Cs-I37, Sr-90 and Am-241. Images were generated from one fallout contaminated sample in which areas were assigned to the dominant isotopes, Sr-90 and Cs-137. The technique allowed an interpretation of the activity distribution in terms of "homogeneous" and "particulate" contamination. 2. A gamma spectroscopic measurement procedure which enables the identification of the presence of hot particles (insoluble radioactive clusters) in large quantities of soil, dirt or dust. In 100 g of a sandy soil originating from 15 km North of the Chernobyl reactor, approximately 500 hot particles were found present, with an estimated Cs-l37 of 20 Bq each. 3. A titration-extraction procedure which identifies radionuclides associated within the humic acid fraction, and their solubility in a range of different extraction solutions. Radiocesium present in peat and sand originating from the Vetka region, was found to have markedly different and lower solubility characteristics compared to similar soil types which were laboratory contaminated using radiocesium in an ionic form. High solubility was found only in fallout contaminated peat, in which 25% of the radiocesium was found to be associated with the humic acid fraction. Depth distributions of gamma emitting radionuclides were determined in soil from the above mentioned locations in Belarus. In peat an exponential depth distribution was obtained, whereas in sandy soil the migration velocity was found to be slower and the depth distribution could not be fitted by a single exponential function. The work presented here supports the hypothesis that the pattern of the activity depth distributions, at distances up to 150 km from the Chernobyl reactor, can substantially arise from hot particle contamination. However, other forms of radioactive insoluble clusters may exist. The development of such clusters or hot particles was observed in a pure quartz sand as well as in an "Ea" horizon material from a humo ferric podzol, after treatment with radiocesium in an ionic form.