Study of Position Sensitivity of Large LaBr 3 :Ce Scintillators Readout by SiPMs

Cerium-doped Lanthanum Bromide (LaBr 3 :Ce) is a very attractive material for scintillation detectors for spectroscopy measurements in nuclear physics thanks to its excellent energy resolution (3% at 662 keV). In some experiments, in order to correct for the Doppler broadening effect, some degree of position sensitivity is required in addition to excellent spectroscopy capability. However, the typical geometry of such crystals, designed to enhance their efficiency (crystal thickness equal of comparable to diameter), and the use of diffuse reflectors on all surfaces but the exit window (to enhance energy resolution), make attaining position sensitivity quite challenging. In this work, we use Monte Carlo simulation to study a reference 3' × 3' LaBr 3 :Ce scintillator read out by an array of SiPMs to evaluate position sensitivity over the full volume of the crystal. The reconstruction of the 3D interaction coordinates of the gamma-ray in the scintillator is performed by means of maximum likelihood method provided by the recently developed ANTS2 toolkit. The simulation study demonstrated feasibility of reconstructing position of a single gamma ray scatter anywhere in the crystal. The expected spatial resolution is no worse than 10 mm FWHM in the SiPM plane and 15 mm FWHM for the depth of interaction for 662 keV gamma rays.