Technique for in situ measurement of Cs-137 deposit in soil under clean protected layer

A method to determine a Cs-137 soil deposit in situ, in case of a contamination protected by a clean soil layer is described. The method is based on measurements and processing of count rates in three energy ranges by a Collimated Spectrum Sensitive Detector. The thickness of an analyzed soil layer is up to 40 g/cm/sup 2/. This value corresponds to three mean free paths (mfp, 1 mfp/spl equiv//spl lambda/) of Cs-137 radiation in the soil. The thickness of the uncontaminated soil layer, covering the contaminated one, may achieve 2/spl lambda/. A minimum detectable soil deposit is about 20 kBq/m/sup 2/. An accuracy of a determination of the deposit is 20%. An estimation of the contaminated soil layer thickness slightly depends on a distribution of the contamination depth. Measurement results are presented and compared with data of a soil sampling. The developed technique is highly effective for mapping of contaminated territories. Cs-137 contamination maps of areas in Belarus and Chelyabinsk region of Russia are presented. The measurements of the Techa river bank contamination detected presence of a secondary contamination transference. This method allows to forecast a change of a dose rate after a decontamination of the territory and to determine rates of necessary rehabilitation and its efficiency.