Increased Dose Rate Precision In Combined Alpha And Beta Counting In The Mu Dose System - A Probabilistic Approach To Data Analysis

The mu Dose system was developed to allow the measurement of environmental levels of natural radioactive isotopes. The system records alpha and beta particles along with four decay pairs arising from successive decays of Bi-214/Po-214, Rn-220/Po-216, Bi-212/Po-212 and Rn-219/Po-215. Under the assumption of secular equilibrium, this allows assessing the specific radioactivities of U-238, U-235, Th-232 day chains and K-40. This assessment provides results with uncertainties which are correlated and, thus, require the development of an error estimation methodology which takes this issue into account. In the current work, we present two different approaches for uncertainty propagation based on Monte Carlo and Bayesian methods. Both approaches produce statistically indistinguishable results and allow significantly better dose rate precision than when the correlations are not accounted for. In the given example, the dose rate precision is improved by a factor of two.