Collimated detector technique for measuring a 137Cs deposit in soil under a clean protected layer

A method to determine the 137Cs soil deposit in situ where the contamination is covered by a clean soil layer is described. The method is based on measurements of the count rates in three energy ranges by a collimated spectrum sensitive detector and their processing. The deposit determination accuracy is 20%. The measurement results are presented and compared with data from soil sampling. The 137Cs contamination maps of areas in Belarus and the Chelyabinsk region of Russia are presented. Measurements of the river Techa bank contamination detected the presence of secondary contamination. This method permits the change of dose rate after land decontamination and the work needed for decontamination and its efficiency to be predicted.