PNNL

Abstract

In low-level radioactivity measurements, it is often important to decide whether a measurement differs from background. A traditional formula, the N13.30 rule, does not adequately account for the discrete nature of the Poisson distribution for paired blank (equal count times for background and sample) measurements, especially at low numbers of counts. We calculate the actual false positive rates that occur using the N13.30 DL formula as a function of a priori false positive rate a and background Poisson mean m = rt, where r is the underlying Poisson rate and t is the counting time. False positive rates exceed a by significant amounts for alpha