Experimental determination of the vertical and horizontal distribution of 137Cs in the ground

The activity of 137Cs in soil was determined by gamma-spectroscopic measurements on several bore cores, sliced in 2–3 cm layers, taken at four places in Sweden. A method of taking the bore cores in a triangular pattern for the dual purpose of minimizing the number of samples as well as the analysis time was investigated and used to determine the vertical and horizontal behaviour of the distribution of 137Cs in soil. It was found that cross contamination and compression of the soil during sampling was negligible. The depth distribution of 137Cs activity, from fallout as well as that from Chernobyl, was found by fitting the experimental points to an exponential function, which was found not to be a simple function of depth. The method of sampling also made it possible to express the depth as linear depth in cm in spite of large variations in soil density. The activity at a given site was shown to be well approximated by a general sample composed of soil from the three bore cores, and the activity uncertainty obtained was about 17%.