Hot particle detection using uncertainties in activity measurements of soil

The uncertainty in gamma spectroscopic activity measurements is investigated for soil containing hot particles. A radioactivity inhomogeneity uncertainty needs to be taken into account, which depends on the density of hot particles in the sample geometry, the distribution of their activities, and the specific source-detector geometry. The maximum activity error due to hot particles in our sampled Chernobyl soil with a 137Cs activity of 100 kBq kg(-1) soil was 6% for our source detector geometry. The methodology presented might have a practical application in nuclear power plants to detect hot particles in a large quantity of dust or dirt. The number of hot particles present can be estimated if the activity of all particles is assumed to be similar. With this assumption 100 g of the investigated soil sample would contain about 500 hot particles with an approximate activity of 20 Bq each.