Position sensitivity in a 3″ × 3″ LaBr3:Ce scintillator

The position sensitivity of a cylindrical continuous 3" × 3" (7.62 cm × 7.62 cm) LaBr₃:Ce crystal was studied using a collimated beam of 662 keV gamma rays and a spectroscopic shielded PMT (HAMAMATSU R6233-100SEL) with standard passive voltage divider (HAMAMATSU E1198-26). The used crystal is sealed in a capsule and has diffusive/reflective surfaces to optimize the energy resolution. A complete scan of the crystal was performed with a 5 mm step grid. The data show that, in average, the image, produced by the scintillation light on the photocathode, changes with the source position. By using the measured full energy peak position using three different windows on the PMT it was possible to identify the position of the interaction of the incident gamma ray.