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 based on the matrix formalism developed by Semkow et al. [Nucl. Instr. and 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 dependence of the efficiencies is approximated by an exponential function, enabling the integrations to be performed analytically. This approach was tested by measuring γ-ray spectra from samples prepared with calibrated activities of 110Agm. Two low volume samples (30 ml) were measured, one as an aqueous solution and the other as a mercury solution of the isotope. In addition a high volume sample (200 ml) was measured to test the method at higher volumes. The calculations show an acceptable agreement with the prepared standards, thus proving the approach as useful method in γ spectrometry.