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

Information relating to the spatial variability of 137Cs inventories within small areas is an important requirement both for assessing environmental contamination associated with the Chernobyl accident and for use in geomorphological applications where 137Cs measurements can provide a basis for estimating 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 sampling. However, in order to assess this potential, there is a need for rigorous comparisons of the results obtained using the two approaches. This contribution reports the results of such a comparison undertaken in the small Lapki Balka catchment (2.18 km2) located near the town of Plavsk in Russia. The study area, which is located ca. 550 km northeast of Chernobyl, received high inputs of Chernobyl fallout and 137Cs inventories immediately after the accident were in excess of 200 kBq m−2. Parallel measurements of 137Cs inventories were made at more than 120 points using a ‘CORAD’ portable detector and conventional soil sampling. The sampling points were selected to be representative of the range of land use and geomorphological features within the study catchment. The results generally showed close agreement between the values of 137Cs inventory provided by the two approaches, but it is necessary to take account of the fact that the ‘CORAD’ results represent spatially averaged values, whereas the analysis of soil cores provides essentially point values. The interaction of the spatial properties of the two sets of measurements with the microvariability of soil 137Cs inventories must be considered when interpreting differences in both magnitude and dispersion. The results obtained indicate that in situ measurement of 137Cs inventories can provide a viable alternative to traditional field sampling in areas with high radiocaesium inventories as a result of the Chernobyl accident. Further work is required to evaluate this potential in areas with lower 137Cs inventories associated with bomb fallout.