The X'tal cube with 1 mm<sup>3</sup> isotropic resolution based on a stack of laser-segmented scintillator plates

Abstract

X'tal cube is the 3D position-sensitive radiation detector we have developed. Its structure uses multi-pixel photon counters (MPPCs) that are coupled on all sides of the scintillation crystal block which is segmented into a 3D array of cubes. No reflector is inserted into the crystal block so that scintillation light originating in one of the cubic segment spreads 3-dimensionally and distributes among all MPPCs on the crystal block. We have already succeeded in identifying 18 × 18 × 18 segments of 1 mm × 1 mm × 1 mm in size with a simple Anger-type calculation of the MPPC signals when we used the crystal block having 3D segmentation inside by laser processing (the 3D crystal block). On the other hand, we have explored the possibility of structuring the crystal block by stacking scintillator plates having 2D segmentation by laser processing (a plate crystal block) instead of the 3D crystal block. The 2D segmentation in thin scintillators is much easier to achieve than the 3D segmentation and in the event that the crystal block has a crack, we can exchange the scintillator partially for the plate crystal block. In our previous study, we proved that the plate crystal block has sufficient segment identification ability for a 9 × 9 × 9 array of 2 mm × 2 mm × 2 mm crystal segments. In this study, we aimed for higher spatial resolution and examined the use of 1 mm thick scintillator plates segmented in an 18 × 18 array of 1 mm × 1 mm elements. We used LYSO for the scintillator. Performance of the plate crystal block was compared with that of the 3D crystal block.