Development of 2D-ACAR apparatus using a new type of position sensitive gamma-ray detectors

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We have constructed a new position sensitive-y -ray detector to be used for the two-dimensional angular correlation of annihilation radiation apparatus. It consists of an array of 2.6*2.6*18mm3 BGO scintillator pieces, a light guide, and metal-package position-sensitive photomultiplier tubes (R5900-00-C8) recently developed by Hamamatsu Photonics Co., Ltd.We first constructed and tested a prototype of the detector using four of the R5900-00-C8 tubes. The separations of the position spectra are excellent except for those of the scintillator pieces which are totally on the insensitive area.We then constructed a large detector whose area was l60mm*l6Omm. It consists of 36 of the photomultiplier tubes, a light guide, and about 3000 BGO scintillator pieces whose sizes are 2.6mm*2.6mm*l8mm. Every other scintillator along the row totally on the insensitive area was replaced by a dead block. By using the BGO scintillators of this length, high detection efficiency of gamma-ray per area is achieved. The spatial resolution is about 3mm and the time resolution is less than 10ns.