On the role of covariances for uncertainty estimates in radioactivity measurements

By means of a few illustrative examples it is demonstrated that covariances (i.e. correlations) can play a role for determining uncertainties in radioactivity counting. The use of the generalised “error-propagation law” for the combination of uncertainties (which allows the treatment of random and non-random uncertainties in the same manner) may be necessary even if only statistical uncertainties are primarily involved in the measurements.