Simulation approach to coincidence summing in γ-rayγ-ray spectrometry

Some of the radionuclides used for efficiency calibration of a HPGe spectrometer are subject to coincidence-summing (CS) and account must be taken of the phenomenon to obtain quantitative results when counting samples to determine their activity. We have used MCNPX simulations, which do not take CS into account, to obtain γ-rayγ-ray peak intensities that were compared to those observed experimentally. The loss or gain of a measured peak intensity relative to the simulated peak is attributed to CS. CS correction factors are compared with those of ETNA and GESPECOR. Application to a test sample prepared with known radionuclides gave values close to the published activities.

► Coincidence summing occurs when the solid angle is increased.
► The loss of counts gives rise to an approximative efficiency curves, this means a wrong quantitative data.
► To overcome this problem we need mono-energetic source, otherwise, the MCNPX simulation allows by comparison with the experiment data to get the coincidence summing correction factors.
► By multiplying these factors by the approximative efficiency, we obtain the accurate efficiency.