Monte Carlo simulation of response function for LaBr3(Ce) detector and its internal-activity

Lanthanum halide scintillator LaBr3(Ce) could potentially improve the performance of spectroscopic systems because of their fine energy resolution in comparison with traditional scintillator materials and a good linearity of the energy response. Monte Carlo simulation of a detector response function presents a very challenging problem especially in 2 MeV region where internal radioisotopes inside the LaBr3(Ce) crystal make the energy response complex structure. The detector response functions of LaBr3(Ce) (38.1 mm × 76.2 mm cylindrical) have been calculated for standard γ-ray sources and internal sources using simulation toolkit GEANT4. The internal activity was investigated in details by comparison simulation results with the experimental. As a result we can reproduce the experimental spectra, however, there is still a few missing sources around 2 MeV region.