X'tal cube detector composed of a stack of scintillator plates segmented by laser processing

We have developed a 3-dimasional (3D) position sensitive radiation detector named "X'tal cube". The X'tal cube is composed of a scintillation crystal block and multipixel photon counters (MPPCs). No reflector is inserted in the crystal block. It is segmented 3 dimensionally into small cubes (3D segmentation) by only optical discontinuity and scintillation light from a segment is detected by all MPPCs which are coupled on all six surfaces of the crystal block. We have already succeeded to make the 3D segmentation inside of a monolithic scintillator block by laser processing technique instead of arranging small cubic scintillator elements into a 3D array as a general way. We obtained the result that utilizing the laser processing technique not only eliminates the difficulty of fabrication with the small scintillator elements but also improves detector performance. As a new trial, we fabricated the crystal block by stacking the scintillator plates which are segmented 2 dimensionally by the laser processing technique (2D segmentation). Plates are also easy to handle compared to the small scintillator elements and for the laser processing, 2D segmentation is much simpler than the 3D segmentation. In this study, we evaluated performance of the X'tal cube with the scintillator plates (Plate-XC) to confirm its feasibility. Performance was measured by irradiating 662 keY gamma-rays. Used scintillator were LYSO plates of 2.0 mm in thick. They had 2D segmentation by laser to make 2.0 mm × 2.0 mm × 2.0 mm segments. Between the plates was chosen as air gap. We coupled a 4 × 4 array of the MPPC to six surfaces of the crystal block. Results showed sufficient performance in crystal identification performance and energy resolution. As a further investigation to understand character of the Plate-XC, scintillation light distribution in the crystal block was also measured. Results indicate that light spread from outer segments is influenced by the segment boundary conditions, air gap or laser processed gap, while the spread from the center segment does not seem to get the influence. In energy performance, around 10% energy resolution was obtained for the outer segments as well as for the center segment.