Monte Carlo simulation of the nonlinear full peak energy responses for gamma-ray scintillation detectors

A Monte Carlo code has been developed, which predicts the nonlinear full peak energy responses of scintillation detectors to incident gamma-rays. It is illustrated here for the popular scintillation detectors, NaI and BGO. The full energy response can be determined by treating the detector as effectively infinite and assuming that all photons and electrons are fully absorbed within the detector. This assumption means that no geometrical direction or position tracking is required, only the selection of sequential photon interactions based on the appropriate energy-dependent interaction cross-sections. The full energy pulse-height response is determined by the sum of the pulse-height responses from all secondary electrons. Results from infinite NaI and BGO detectors indicate that even though the maximum difference in electron scintillation efficiency is about the same for the two scintillation detectors, the overall effect on the extent of the difference in pulse height is much less for BGO than NaI. This result is due to the larger density and effective atomic number of BGO, which causes significantly fewer Compton scattering events. Compton scattering interactions reduce the incident photon energy without absorption and therefore give more responses at reduced energy where the electron scintillation efficiency is most different.