Corrections of counting losses in gamma-spectrometry of short-lived radionuclides

A short-lived radionuclide is characterized essentially by the decrease of its activity even while it is counted. The relations used between the number of counts recorded in a given time and the half-life in order to obtain the true counting rate are reviewed. Moreover, in gamma-spectrometry with multichannel analysers having variable dead-time, counting losses are observed. Exact corrections are calculated for pure short-lived radionuclides and for mixtures of one short-lived and one or more long-lived radionuclides. Based on these calculations, the approximations given by the built-in “live-timer” device of the analysers and by a new “actual-time” concept (with external live-time measurement) are evaluated. Curves are drawn as functions of the ratio counting time vs. half-life, to ensure minimal errors of less then 1%.