Considerations on the 11th Symposium

This paper presents the results of our measurements and detailed simulations using GEANT4 to investigate the performance of LaBr3:Ce detectors. In the first part of the paper we present the results of our experimental studies using cylindrical 1in.×1in.LaBr3:Ce scintillator. We have measured the energy and timing resolutions and also the absolute detection efficiencies, both, total detection and photopeak, using known activity sources. The energy dependence of the resolution has been studied using a variety of low energy gamma rays sources. The measured absolute efficiencies have been compared with the simulated values using GEANT4. We have extended our simulations to reproduce the recent measurements (Favalli et al., 2008) [15] of absolute photopeak efficiencies of a 1.5in.×1.5in. cylindrical LaBr3:Ce detector up to 5 MeV. The second part of the paper is devoted to a detailed comparative study of the energy dependent absolute efficiencies, both total detection and photopeak, of cylindrical LaBr3, NaI(Tl), and BaF2 scintillators of different sizes for a wide range of gamma rays from 662 keV to 50 MeV. We have also simulated the energy dependent efficiencies for compact assemblies of: (a) LaBr3:Ce and NaI(Tl) and (b) LaBr3:Ce and BaF2 in two different configurations. The efficiencies, so simulated, for these configurations, have been compared with the efficiencies of single scintillators of equivalent volumes. The usefulness of such combined detector assemblies using LaBr3 crystals of available volumes with NaI(Tl)/BaF2 in measurements of high-energy gamma rays (5–50 MeV) is discussed.