Application of a field-portable scintillation detector for studying the distribution of Cs-137 inventories in a small basin in Central Russia

Information relating to the spatial variability of Cs-137 inventories withi n small areas is an important requirement both for assessing environmental contamination associated with the Chernobyl accident and for use in geomorp hological applications where Cs-137 measurements can provide a basis for es timating rates of erosion and sedimentation. Collection of such information using traditional techniques is, however, hampered by the need to collect soil cores and to analyse these in the laboratory using gamma spectrometry, which commonly involves lengthy count times. The use of field-portable in situ detectors offers many potential advantages over conventional field sam pling. However, in order to assess this potential, there is a need for rigo rous comparisons of the results obtained using the two approaches. This con tribution reports the results of such a comparison undertaken in the small Lapki Balka catchment (2.18 km(2)) located near the town of Plavsk in Russi a. The study area, which is located ca. 550 km northeast of Chernobyl, rece ived high inputs of Chernobyl fallout and Cs-137 inventories immediately af ter the accident were in excess of 200 kBq m(-2). Parallel measurements of Cs-137 inventories were made at more than 120 points using a 'CORAD' portab le detector and conventional soil sampling. The sampling points were select ed to be representative of the range of land use and geomorphological featu res within the study catchment. The results generally showed close agreemen t between the values of Cs-137 inventory provided by the two approaches, bu t it is necessary to take account of the fact that the 'CORAD' results repr esent spatially averaged values, whereas the analysis of soil cores provide s essentially point values. The interaction of the spatial properties of th e two sets of measurements with the microvariability of soil Cs-137 invento ries must be considered when interpreting differences in both magnitude and dispersion. The results obtained indicate that in situ measurement of Cs-1 37 inventories can provide a viable alternative to traditional field sampli ng in areas with high radiocaesium inventories as a result of the Chernobyl accident. Further work is required to evaluate this potential in areas wit h lower Cs-137 inventories associated with bomb fallout. (C) 1999 Elsevier Science Ltd. All rights reserved.