Development of the X´tal Cube: A 3D Position-Sensitive Radiation Detector With All-Surface MPPC Readout

We have developed a new three-dimensional (3D) position sensitive radiation detector, called the X´tal cube. The X´tal cube is composed of a scintillation crystal block and a number of multi-pixel photon counters (MPPCs) which are coupled on all six sides of the block. The block is segmented into cubes and no reflector is used between the segments. Scintillation light originating in a crystal segment accordingly propagates three-dimensionally along the alignment of the crystal segments and is efficiently detected by the MPPCs. The X´tal cube could be used as the detector element of a PET system, for instance. We constructed two prototypes of the X´tal cube and evaluated their performance using gamma-ray sources. The crystal block of each prototype is composed of a 3D array of Lu_2xGd_2(1-x)SiO₅: Ce (LGSO, x = 0.9) crystal segments. Each crystal volume is 3.0 mm × 3.0 mm × 3.0 mm. MPPCs of a 3.0 mm × 3.0 mm active area are coupled to each surface of the crystal block. In this work, we show that all crystal segments are identified by a simple Anger-type calculation performed on the MPPC signals for both prototypes. The X´tal cube provides high spatial resolution in three dimensions regardless of the incident angle of the radiation.