Models for the vertical migration of 137Cs in the ground — a field study

Soil sampling was performed repeatedly at two locations in southern Sweden in order to study the behaviour of 137Cs at different times after deposition. At two locations in the city of Lund, in southern Sweden, sampling was done 5 and 7 years after the Chernobyl accident. The samples were analysed for 137Cs from nuclear weapons tests as well as 137Cs of Chernobyl origin and three different models were used to describe the vertical transport in the ground. The first study shows that the downward transport of caesium from the Chernobyl accident with time could be quantified in a simple model, valid for a few years of transport. In another model the relative amount of 137Cs at different depths was observed to change with time in a predictable way and the depth of maximum activity was shown to move downwards with a mean speed of 0•2 cm year-1. A simple compartment model has also been tested.