A probabilistic description of radioactive contamination: a multivariate model.

A multivariate discrete probability model is used to facilitate the description of gamma-ray spectroscopic data obtained from radioactively contaminated territory, east of the former Semipalatinsk nuclear test site in Kazakhstan. Two possible estimators of probabilities of interest have been considered: maximum likelihood and unbiased estimators. We show that unbiased estimators are much easier to compute. The model was used in two variants: (i) several radionuclides in spatially independent measurements, (ii) a single radionuclide in spatially dependent measurements. We show that, in both cases, it is important to take into account the correlation for the accurate evaluation of probabilities of interest.