Determination of the coincidence summing gamma spectrum of a 60Co source by Monte Carlo simulations taking into account the angular correlation γ - γ

Abstract

The coincidence summing effects can remove counts of the photo-peaks or eventually add spurious counts to them when two photons of lower energy interact simultaneously with the detector. Programs that simulate radiation transport generally do not consider simultaneity effects since they simulate one particle at a time. However, it is possible to obtain the coincidence summing spectrum from the simulated spectrum of the particles of each energy individually. The objective of this work is to develop a method to obtain the coincidence summing spectrum of a radioactive source that emits two (or more) photons in cascade. To do this, we have obtained an exact expression for the coincidence summing spectrum based on the probabilities of interaction with the detector of each photon. These probabilities were obtained by MC simulation and from them, the coincidence summing spectrum was obtained by convolution between them. To make the calculation more consistent with the real phenomenon we have taken into account the angular correlation between the photons. Although the method is applied to a ${}^{60}Co$ source, the methodology is valid for the case of volumetric sources of different sizes and shapes and the generalization to the case of sources that emit three or more photons in their decay is immediate.