Calibration of a field-portable gamma detector to obtain in situ measurements of the Cs-137 inventories of cultivated soils and floodplain sediments

Over the past 10 years, a number of studies have exploited the potential fo r using measurements of fallout Cs-137 inventories to document rates and pa tterns of soil erosion on cultivated land and to estimate rates of overbank sedimentation on river floodplains. Traditional procedures for applying th e Cs-137 technique involve the collection of soil or sediment cores from a study site and their subsequent transfer to the laboratory for preparation and analysis by gamma spectrometry. Such procedures are time consuming and there may be a considerable delay before the results are available. It is t herefore difficult to obtain preliminary results, which could be used to gu ide the development of an ongoing sampling programme. The use of in situ ga mma spectrometry measurements to quantify Cs-137 inventories in soils and s ediments offers a number of potential advantages over traditional procedure s. However, in order to derive a reliable estimate of the Cs-137 inventory for a measurement point, it is necessary to take account of the attenuation of Cs-137 gamma rays by the soil matrix and information on the depth distr ibution of Cs-137 i, the soil or sediment is therefore required. In the pre sent study, empirical relationships between in situ measurements of Cs-137 activity and total Cs-137 inventories have been established for soils from a cultivated field and for floodplain sediments, based on information on th e vertical distribution of Cs-137 in the soils and sediments provided by th e forward scattering ratio derived from the field measured spectra. These r elationships have been used to estimate Cs-137 inventories from in situ mea surements of Cs-137 activity at other locations. (C) 2000 Elsevier Science Ltd. All rights reserved.