Performance of a monolithic LaBr 3 :Ce crystal coupled to an array of silicon photomultipliers

A gamma-ray detector composed of a single 28×28×20mm3 LaBr3:Ce crystal coupled to a custom built 4×4 array of silicon photomultipliers was tested over an energy range of 30keV to 9.3MeV. The silicon photomultipliers were initially calibrated using 20ns light pulses generated by a light emitting diode. The photodetector responses measured as a function of the number of incident photons were found to be non-linear and consistent with model predictions. Using corrections for the non-linearity of the silicon photomultipliers, the detector showed a linear response to gamma-rays with energies from 100keV to the maximum available energy of 9.3MeV. The energy resolution was found to be 4% FWHM at 662keV. Despite the large thickness of the scintillator (20mm) and a 5mm thick optical window, the detector was capable of measuring the positions of the gamma-ray interaction points. The position resolution was measured at 356keV and was found to be 8mm FWHM in the detector plane and 11mm FWHM for the depth of interaction. The detector can be used as a building block of a larger calorimeter system that is capable of measuring gamma-ray energies up to tens of MeV.