Background energy spectra for LSO/LYSO scintillation crystals of different geometries

Abstract

The background energy spectrum of lutetium oxyorthosilicate/lutetium yttrium oxyorthosilicate scintillation crystals used in positron emission imaging systems is a research topic of great interest owing to the possibility of using its structure to perform detector calibration and quality control without the need of using external radiation sources. In this paper, the background energy spectra for crystals of different sizes and geometries, including cuboids, frusta, cylinders, tetrahedra, and spheres, have been computed. This was done using a previously developed analytical model that requires the photon absorption probabilities for each shape, obtained through simulations using the PENELOPE Monte Carlo code. It has been found that crystals of different geometries, but with the same volume-to-surface area ratio, give rise to very similar background energy spectra, simplifying its computation. In addition, simple ray tracing simulations were performed, and a robust geometrical model was devised to investigate the geometrical grounds of this practical and compelling result.