Designing position sensitive NaI(Tl) bar-detectors with an empirical model

In 1-D position sensitive bar-detectors, multiple internal reflections and edge effects of scintillation light cause excessive light spread and lead to poor intrinsic spatial resolution along the length of the detector. An empirical model to evaluate surface treatment techniques in containing light spread is developed. In this model, a Lucite bar and a light-emitting diode (LED) are used to simulate light propagation and refraction in a NaI(Tl) bar-detector. Light sensors are placed above the exit window, with an air gap, for spatial recording of light refracted out of the bar. Among the eleven different combinations of surface treatments evaluate, three-side transverse sanding is the compromise between light spread and total light output. These results are confirmed by experiments performed on NaI(Tl) bar-detectors. This model could be a valuable tool to guide the design of position sensitive NaI(Tl) bar-detectors