Performance of the most recent avalanche photodiodes for future X-ray and gamma-ray astronomy

摘要

We report on the performance of the most recent avalanche photodiodes produced by Hamamatsu Photonics, as low-energy X-rays and γ-rays detectors. APDs share good features of both photo diodes and PMTs, as they are very compact, produce an internal gain of 10—100, and have high quantum efficiency close to 100% in the visible right. Until very recently, however, APDs were limited to very small surfaces, and were mainly used as a digital device for light communication. We have developed large area (up to 10x10 mm~2) APDs which can be used in the physics experiments. The best energy resolution of 6.4% (FWHM) was obtained in direct detection of 5.9 keV X-rays. The FWHM results of 9.4% and 4.9% were obtained for 59.5 keV and 662 keV γ-rays respectively, as measured with the CsI(Tl) crystal. The minimum detectable energy for the scintillation light was as low as 1 keV at lightly cooled environment (—20°C). Note that our results are the best records ever achieved with APDs. Various applications of APDs are presented for future space research and nuclear medicine. In particular 2-dimensional APD arrays will be a promising device for a wide-band X-ray and γ-ray imaging detector.