Performance of large-area avalanche photodiode for low-energy X-rays and γ-rays scintillation detection

We report on the performance of large-area (5×5 mm2) avalanche photodiodes (APD) produced by Hamamatsu Photonics, as a low-energy X-rays and γ-rays scintillation detector. Hamamatsu APD has a reverse structure and works at relatively low bias voltage of 300–350 V. The leakage current is 1.2 nA at room temperature (25°C) and decreases to 10 pA at −20°C for an avalanche gain of 50. The best FWHM energy resolutions of 9.4±0.3% and 7.4±0.3% were obtained for 59.5 keV γ-rays from 241Am and 122 keV γ-rays from 57Co sources, respectively, as measured with a 5×5×5 mm3 cubic CsI(Tl) crystal. We show that the minimum detectable energy for the scintillation light is remarkably low; 4.6 keV at room temperature (20°C) and 1.1 keV at −20°C. 5.9 keV X-rays from 55Fe were clearly resolved at −20°C with an FWHM resolution of 32.9±0.3%. These results suggest that Hamamatsu APD can be a promising device for future applications in low-energy scintillation detection.