Study of large area Hamamatsu avalanche photodiode in a γ-ray scintillation detector

We have carried out study of a large area (10×10mm2), reverse-type avalanche photodiode (APD) recently developed by Hamamatsu photonics. It has low dark current of 3 nA at room temperature, and the gain stability was almost the same as prototypical APDs reported in our previous paper. We studied the performance as a γ-ray detector with four scintillators, CsI(Tl), BGO, GSO(Ce), and YAP(Ce) crystals. For example we obtained the best energy resolution of 4.9±0.2% (FWHM) for 662 keV γ-rays, as measured with a 10×10×10mm3 CsI(Tl) crystal. The minimum detectable energy was as low as 10 keV at 20°C and 3.1 keV at -20°C. Thanks to its large effective area, this APD can effectively read out photons from larger size scintillators. When coupling to a 300×48mm2 BGO plate of 3 mm thickness, an FWHM energy resolution of 20.9±0.2% was obtained for 662 keV γ-rays, with the minimum detectable energy of about 60 keV at -15°C. These results suggest that our prototype APD can be a promising device for various applications replacing traditional PMTs such as use in space for Japan's future X-ray astronomy mission NeXT.