A.V. Chesnokov, A.P. Govorum, O.P. Ivanov, V.I. Liksonov, S.V. Smirnov, V.N. Potapov, V.N. Fedin, S.B. Shcherbak & L.I. Urutskoev (RECOM Ltd., Schukinskaya St. 12-1, Moscow, 123182, Russia)

The technique to determine Cs-137 soil deposit in site is described. It is based on a processing of gamma energy spectrum measured by a collimated gamma spectrometric radiometer (CSR). The thickness of analyzed layer is 3 mean free path (mfp) of Cs-137 radiation in the soil. The technique allows to determine a thickness of upper soil layer containing more then 80% of a total Cs-137 stock. The thickness of uncontaminated soil layer covering a contaminated one may achieve 2 mfp. The new portable CSR was developed for measurements. The detectable soil deposit minimum of CSR is 20 kBq/sq.m and accuracy is near 15%. The data obtained for contaminated territories in former USSR shows good agreement with results of traditional measuring methods. The developed technique is effective for landscape gamma radiation survey because of its simplicity and high productivity. The CSR measurements of activity density of natural nuclides (Ra-226, Th-232, K-40) and manmade ones (Eu-154, Co-60) show its efficiency for study of mine wastes and complex gamma-nuclides contamination. The river's bank contamination anomaly were investigated. It was shown that the high contaminated areas of bank territory exist due to gathering of deposit from water surface. The high spatial resolution and possibility to measure the contamination penetration depth allow to make scale analysis of deposit and to distinguish the initial contamination from secondary one (result of human activity).