ACTIVITY CALCULATION FOR VOLUMINOUS SAMPLES IN THE PRESENCE OF COINCIDENCE SUMMING EFFECTS

A method for calculation of the activity of voluminous samples in the presence of coincidence summing effects is presented. The method is ba sed on the matrix formalism developed by Semkow et al. [Nucl. Instr. a nd Meth. A 290 (1990) 437]. In the expressions connecting count rates with the properties of the decay scheme and the detector, the products of the efficiencies were substituted by the integrals of efficiencies over the sample. To avoid many numerical integrations, the spatial. d ependence of the efficiencies is approximated by an exponential functi on, enabling the integrations to be performed analytically. This appro ach was tested by measuring gamma-ray spectra from samples prepared wi th calibrated activities of Ag-110(m). Two low volume samples (30 ml) were measured, one as an aqueous solution and the other as a mercury s olution of the isotope. In addition a high volume sample (200 ml) was measured to test the method at higher volumes. The calculations show a n acceptable agreement with the prepared standards, thus proving the a pproach as useful method in gamma spectrometry.