In situ method to determine depth distribution of buried activity

A method is described to determine the depth distribution of buried activity offering an alternative to conventional soil sampling and laboratory analysis by in situ measurements with small detectors inserted into the ground. As a demonstration of the method small-scale variations in the distribution of (137)Cs in a riparian marsh in central-eastern Sweden are determined using lanthanum bromide detectors (LaBr₃). The results show variations of the activity ranging between 400 and 2200 kBq/m² over an area not exceeding 350 m². The decrease of the average activity since 2003 coincides with the physical decay indicating that no net redistribution of activity into this part of the marsh has occurred during the intervening years.