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Application of in-situr measurement to determine 137Cs in the Swiss Alps
Journal
Journal of environmental radioactivity
Volume
101
Number
5
Pages / Article-Number
369-76
Keywords
Nal detector, GeLi detector, Alps, In-situ measurements, Field application
Abstract
Establishment of Cs-137 inventories is often used to gain information on soil stability. The latter is crucial in mountain systems, where ecosystem stability is tightly connected to soil stability. In-situ measurements of Cs-137 in steep alpine environments are scarce. Most studies have been carried out in arable lands and with Germanium (Ge) detectors. Sodium Iodide (Nal) detector system is an inexpensive and easy to handle field instrument, but its validity on steep alpine environments has not been tested yet. In this study, a comparison of laboratory measurements with GeLi detector and in-situ measurements with Nal detector of Cs-137 gamma soil radiation has been done in an alpine catchment with high Cs-137 concentration (Urseren Valley, Switzerland). The aim of this study was to calibrate the in-situ Nal detector system for application on steep alpine slopes. Replicate samples from an altitudinal transect through the Urseren Valley, measured in the laboratory with a GeLi detector, showed a large variability in Cs-137 activities at a meter scale. This small-scale heterogeneity determined with the GeLi detector is smoothed out by uncollimated in-situ measurements with the Nal detector, which provides integrated estimates of Cs-137 within the field of view (3.1 m(2)) of each measurement. There was no dependency of Cs-137 on pH, clay content and carbon content, but a close relationship was determined between measured Cs-137 activities and soil moisture. Thus, in-situ data must be corrected for soil moisture. Close correlation (R-2 = 0.86, p < 0.0001) was found for Cs-137 activities (in Bq kg(-1)) estimated with in-situ (Nal detector) and laboratory (GeLi detector) methods. We thus concluded that the Nal detector system is a suitable tool for in-situ measurements in alpine environments. This paper describes the calibration of the Nal detector system for field application under elevated Cs-137 activities originating from Chernobyl fallout. (C) 2010 Elsevier Ltd. All rights reserved.
