On the performance of large monolithic LaCl₃(Ce) crystals coupled to pixelated silicon photosensors

Abstract

We investigate the performance of large area radiation detectors, with high\nenergy- and spatial-resolution, intended for the development of a Total Energy\nDetector with gamma-ray imaging capability, so-called i-TED. This new\ndevelopment aims for an enhancement in detection sensitivity in time-of-flight\nneutron capture measurements, versus the commonly used C6D6 liquid\nscintillation total-energy detectors. In this work, we study in detail the\nimpact of the readout photosensor on the energy response of large area (5050\nmm2) monolithic LaCl3(Ce) crystals, in particular when replacing a conventional\nmono-cathode photomultiplier tube by an 88 pixelated silicon photomultiplier.\nUsing the largest commercially available monolithic SiPM array (25 cm2), with a\npixel size of 66 mm2, we have measured an average energy resolution of 3.92%\nFWHM at 662 keV for crystal thicknesses of 10, 20 and 30 mm. The results are\nconfronted with detailed Monte Carlo (MC) calculations, where both optical\nprocesses and properties have been included for the reliable tracking of the\nscintillation photons. After the experimental validation of the MC model, se\nuse our MC code to explore the impact of different a photosensor segmentation\n(pixel size and granularity) on the energy resolution. Our optical MC\nsimulations predict only a marginal deterioration of the spectroscopic\nperformance for pixels of 33 mm2.\n