Summing coincidence in rare event gamma-ray measurements under an ultra-low background environment

A Monte Carlo method based on the GEANT4 toolkit has been developed to correct the full-energy peak (FEP) efficiencies of a high purity germanium (HPGe) detector equipped with a low background shielding system, and moreover evaluated using summing peaks in a numerical way. It is found that the FEP efficiencies of $^{60}$Co, $^{133}$Ba and $^{152}$Eu can be improved up to 18\% by taking the calculated true summing \mbox{coincidence} factors (TSCFs) correction into account. Counts of summing coincidence $\gamma$ peaks in the spectrum of $^{152}$Eu can be well reproduced using the corrected efficiency curve within an accuracy of 3\%.