Crystal identification performance of the jPET detector depending on refractive index of optical cement between scintillators

Previously we developed the four-layer DOI detector which consists of four layers of scintillation crystal arrays and a position sensitive photomultiplier tube (PS-PMT). To control the behavior of scintillation light in each DOI crystal array, some reflectors between crystals are removed so that all crystal responses in the four layers are expressed in one two-dimensional (2D) position histogram by implementing an Anger-type calculation of the PS-PMT signals. Since the method utilizes spread of scintillation light through the space between crystals with no reflectors, positioning performance in the 2D position histogram depends on the crystal dimensions, the crystal surface finish, and refractive index of the material in the space. That indicates the degradation of positioning performance as the result of changing crystal condition can be mitigated by using an optical cement of appropriate refractive index. In this work, we studied crystal identification performance by using an optical cement of variable refractive index. The results reveal that 2D position histogram changes as a function of the refractive index change of the optical cement between crystals.