Simulation of light output from narrow sodium iodide detectors

The use of narrow scintillators in imaging devices raises the question of whether there is enough light output that can yield reasonable energy and spatial resolutions. Compared to scintillation within large-area detectors (such as those used in conventional gamma cameras), scintillation photons within narrow detectors are expected to undergo more reflections because of the proximity of the detector surfaces. In this study, we use simulation methods to estimate the light output from long, narrow sodium iodide crystals, and to investigate the effects of detector geometry and detector surface reflection properties on the fraction of scintillation photons that are able to leave the crystal through the exit window (on one of the long, narrow sides). Our simulations show that the light output from a 3.5-mm wide by 10-mm high by 300-mm long detector can result in reasonable energy resolutions. Our simulations also suggest that, in conjunction with the use of external reflectors, a crystal that has its sides polished to a smooth finish results in better light output than one with sides grounded to a rough finish.