The role of covariance in the analysis of gamma-ray spectra

The classification of photopeaks and the relationship of peak area to nuclide activity are discussed. Two procedures for activity estimation are described: one of them deals with the special case of activity estimation for a single nuclide, where unresolved photopeaks are absent or neglected; the other one deals with simultaneous activity estimation using all the photopeaks associated with an interrelated group of nuclides. Both procedures take correlations into account. (author)