Comparative estimations of 137Cs distribution in a boreal forest in northern Sweden using a traditional sampling approach and a portable NaI detector

Field-portable detectors have been frequently used in routine monitoring and hazard assessment studies. However, there have been few thorough attempts to evaluate their potential as an alternative to the traditional procedure of collecting samples and analysing them in the laboratory. Thus, in this study the two approaches were compared in terms of their utility for monitoring Cs-137 activity in the Nyanget catchment in northern Sweden. The objectives were: (i) to determine the Cs-137 activity in soils associated with three types of vegetation, (ii) to map the geographical distribution Of (CS)-C-137 using the portable NaI detector connected to a GPS system (GDM-40), (iii) to identify Cs-137 anomalies in the catchment, and (iv) to compare the measurements obtained with the NaI detector and traditional sampling followed by laboratory analysis. Our results demonstrate that the GDM-40 has very good potential for making (CS)-C-137 inventories and for detecting Cs-137 anomalies within large areas. The GDM-40 measurements identified differences between different hydrological areas that were not determined with the soil sampling method. The GDM-40 method is much faster than a traditional soil sampling method. However, soil sampling cannot be totally excluded because it is needed to calibrate the GDM-40. The agreement between the Cs-137 activity values obtained by the two approaches was 20% which is good in the field where so many factors vary. (c) 2006 Elsevier Ltd. All rights reserved.