Comparative measurements on LaBr3(Ce) and LaCl3(Ce) scintillators coupled to PSPMT

We present the results of energy resolution measurements at 662 keV for a LaBr₃ crystal (3.67%) and a 6×6 array of LaCl₃ crystals (4.65%) coupled to a 5" diameter Hamamatsu PSPMT, and compare them to measurements on arrays of NaI (7.37%) and BGO (16.07%). The raw spectra obtained using the full PSPMT area were less impressive due to the well-known position-dependent sensitivity of the PSPMT. The raw energy resolution of the total area of LaCl₃ without collimation is poor (13%) but it is much improved by position dependent gain correction (5.85%). To avoid this complication, the spectra were acquired using a well-collimated source focused upon a small area of the detector. 2D flood-field radiation images from those scintillators were also obtained. The position distortion due to the light spreading in the scintillator and the non-uniformity of the PSPMT were corrected by several methods. Gaussian fitting was found to be superior to other methods but at the expense of increased processing time.