Development of high-resolution gamma detector using sub-mm GAGG crystals coupled to TSV-MPPC array

摘要

In this study a high-resolution gamma detector based on an array of sub-millimeter Ce:GAGG (Cerium doped Gd_3Al_2Ga_3O_(12)) crystals read out by an array of surface-mount type of TSV-MPPC was developed. MPPC sensor from Hamamatsu which has a 26 by 26 mm~2 detector area with 64 channels was used. One channel has a 3 by 3 mm~2 photosensitive area with 50 μm pitch micro cells. MPPC sensor provides 576 mm~2 sensing area and was used to decode 48 by 48 array with 0.4 by 0.4 by 20 mm~3 Ce:GAGG crystals of 500 μm pitch. The base of the detector with the crystal module was mounted to a read out board which consists of charge division circuit, thus allowing for a read out of four channels to identify the position of the incident event on the board. The read out signals were amplified using charge sensitive amplifiers. The four amplified signals were digitized and analyzed to produce a position sensitive event. For the performance analysis a ~(137)Cs source was used. The produced events were used for flood histogram and energy analysis. The effects of the glass thickness between the Ce:GAGG and MPPC were analyzed using the experimental flood diagrams and Geant4 simulations. The glass between the scintillator and the detector allows the spread of the light over different channels and is necessary if the channel’s sensitive area is bigger than the scintillator’s area. The initial results demonstrate that this detector module is promising and could be used for applications requiring compact and high-resolution detectors. Experimental results show that the detectors precision increases using glass guide thickness of 1.35 mm and 1.85 mm; however the precision using 2.5 mm are practically the same as if using 0.8 mm or 1.0 mm glass guide thicknesses. In addition, simulations using Geant4 indicate that the light becomes scarcer if thicker glass is used, thus reducing the ability to indicate which crystal was targeted. When 2.5 mm glass thickness is used, the scarce light effect becomes dominant for the precision of the detector.