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The performance of the large area reach-through avalanche photodiode (APD), manufactured by Hamamatsu Photonics, K.K. as a high resolution X-ray detector is presented. The mentioned APD has an area of 3 mm ∅ , a fast time response for signal carrier collection and its thick depletion layer of 130 μ m shows a potential to be used as an effective X-ray absorber below 20 keV. Having a capacitance of ∼ 10 pF and a low dark current of 5 nA for a gain of 15, at room temperature, this APD had demonstrated one of the best energy resolutions within this kind of devices: 6.4% (FWHM) for 5.9 keV photons with a minimum detectable energy of 0.3 keV, measured at - 20 ∘ C . The experiments for the timing property were made in a synchrotron beam facility using an 8 keV X-ray beam; the reached count rate was above 10 8 counts/s, corresponding to a very short dead time of 4.5 ns/pulse. In order to test the radiation hardness of the APD, the device was irradiated at a Ring Cyclotron Facility with a 53.5 MeV proton beam. The total dose was of 11.3 krad and no fatal damage was found in the APD, although the dark current of the APD had shown an increase of one order of magnitude. Finally, the obtained results allow us to affirm that the reach-through APD has the potential to become an excellent X-ray detector, especially in the space mission application.

Avalanche photodiodes (APDs) are promising light sensor for various fields of experimental physics. It has been argued, however, that variation of APD gain with temperature could be a serious problem preventing APDs from replacing traditional photomultiplier tubes (PMTs) in some applications. Here we develop an active gain-control system to keep the APD gain stable under moderate temperature variations. As a performance demonstration of the proposed system, we have tested the response of a scintillation photon detector consisting of a 5x5 mm^2 reverse-type APD optically coupled with a CsI(Tl) crystal. We show that the APD gain was successfully controlled under a temperature variation of DT = 20deg, within a time-cycle of 6000 sec. The best FWHM energy resolution of 6.1+-0.2 % was obtained for 662 keV gamma-rays, and the energy threshold was as low as 6.5 keV, by integrating data from +20deg - 0deg cycles. The corresponding values for -20deg - 0deg cycles were 6.9+-0.2 % and 5.2 keV, respectively. These results are comparable, or only slightly worse than that obtained at a fixed temperature. Our results suggest new potential uses for APDs in various space researches and nuclear physics. As examples, we briefly introduce the NeXT and Cute-1.7 satellite missions that will carry the APDs as scientific instruments for the first time., 14 pages, 10 figures, accepted by NIM-A

The avalanche photodiodes (APDs) have attracted considerable attention in various field of experimental physics, but their uses are still limited in only a few experiments, possibly due to their small surface areas. Here, we report the development of the large-area ( ∼ 20 mm square) APDs, for future applications to high-resolution X-rays and γ -rays detection. We have made two prototypes of reverse-type APDs based on different concepts, one consists of a 2 × 2 array of 10 × 10 mm 2 pixels (APD1) and the other is a monolithic pixel of 19 × 19 mm 2 size (APD2) to achieve a large effective area. By comparing the dark current and gain characteristics at room temperature ( + 20 ∘ C ) and lightly cooled environment ( - 20 ∘ C ), we quantitatively discussed the origin of predominant noise source at different temperatures. As a performance demonstration of newly developed APDs, we made a scintillation γ -ray detector consisting of a 20 × 20 × 5 mm 3 CsI(Tl) crystal and a 2 cm-square APD. The best FWHM energy resolution of 5.5 ± 0.2 % were obtained for 662 keV γ -rays at room temperature. Similarly, the best FWHM energy resolution of 8.5 ± 0.2 % were obtained for 122 keV γ -rays at lightly cooled environment. We showed that the minimum detectable energy for scintillation light was 15 keV at 20 ∘ C and less than 5 keV at - 20 ∘ C .

We have studied the performance of large area avalanche photodiodes (APDs) recently developed by Hamamatsu Photonics K.K, in high-resolution X-rays and Gamma-rays detections. We show that reach-through APD can be an excellent soft X-ray detector operating at room temperature or moderately cooled environment. We obtain the best energy resolution ever achieved with APDs, 6.4 % for 5.9 keV X-rays, and obtain the energy threshold as low as 0.5 keV measured at -20deg. Thanks to its fast timing response, signal carriers in the APD device are collected within a short time interval of 1.9 nsec (FWHM). This type of APDs can therefore be used as a low-energy, high-counting particle monitor onboard the forthcoming Pico-satellite Cute1.7. As a scintillation photon detector, reverse-type APDs have a good advantage of reducing the dark noise significantly. The best FWHM energy resolutions of 9.4+-0.3 % and 4.9+-0.2 % were obtained for 59.5 keV and 662 keV Gamma-rays, respectively, as measured with a CsI(Tl) crystal. Combination of APDs with various other scintillators (BGO, GSO, and YAP) also showed better results than that obtained with a photomultiplier tube (PMT). These results suggest that APD could be a promising device for replacing traditional PMT usage in some applications. In particular 2-dim APD array, which we present in this paper, will be a promising device for a wide-band X-ray and Gamma-ray imaging detector in future space research and nuclear medicine., Comment: 11 pages, 7 figures, accepted by NIM-A

We have carried out study of a large area ( 10 × 10 mm 2 ) , 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 × 10 mm 3 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 × 48 mm 2 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.

We report on the performance of large-area (5×5 mm 2 ) 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 241 Am and 122 keV γ-rays from 57 Co sources, respectively, as measured with a 5×5×5 mm 3 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 55 Fe 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.

Cute-1.7 is a pico-satellite mainly developed by students at Tokyo Institute of Technology (Tokyo Tech). This will be the second satellite built at Tokyo Tech after the first one, CUTE-I, which was launched in June 2003. The configuration of Cute-1.7 is a 10 cm × 10 cm × 20 cm box with a mass of 2 kg. The engineering objective of Cute-1.7 is to validate commercially available products such as Personal Digital Assistances (PDAs) in the space environment, and to demonstrate a "satellite core concept" which is dividing a satellite into a bus component and a mission component to adopt various missions. The scientific objective is to demonstrate the performance of avalanche photo diodes (APDs) as future X-ray detectors used in the space environment. Results of this mission will provide the first feedback for a space application of APD such as Japan's future X-ray astronomy mission NeXT.

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 a 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 mm2) 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.

We report on the performance of recent avalanche photodiodes (APDs) produced by Hamamatsu photonics as a new X-ray and γ-ray detector. An FWHM energy resolution of 6.5% was obtained for direct detection of 5.9 keV X-rays,whereas 9.4% was obtained for 59.5 keV γ-rays measured with a CsI crystal. Because of their small volumes and low operating bias voltage, APDs are promising devices for future space research. We are planning to use them for our small satellites, CUTE-1.7 and Hu-ring.

The Cute-1.7 was launched successfully in February 2006 as a piggyback satellite of the Astro-F mission. The Cute-1.7 dimensions are 10 × 10 × 20 cm 3 box with a total mass of 3.6 kg. It is the second pico-satellite to have been developed completely by students of the Tokyo Institute of Technology (Tokyo Tech.) after the successful launch of the CUTE-I in June 2003. The goals of the Cute-1.7 mission are two-fold: (1) to validate high-performance, commercially available products for the first time in space. We particularly use personal digital assistants (PDAs) as a main computer in orbit (2) to demonstrate new potential uses for small satellites in various space studies, as proposed by the “satellite-core” concept. For the Cute-1.7 mission, we will carry avalanche photo diodes (APDs) as a high-count particle monitor in low-Earth orbit. Here we present details of various ground tests and pre-flight performance of the Cute-1.7 immediately before the launch. Results of the Cute-1.7 mission will provide quick feedback for space applications of APDs in Japan's future X-ray astronomy mission NeXT.

The Polarized Gamma-ray Observer (PoGO) is a new balloon-borne instrument designed to measure polarization from astrophysical objects in the 30-200 keV range. It is under development for the first flight anticipated in 2008. PoGO is designed to minimize the background by an improved phoswich configuration, which enables a detection of 10 % polarization in a 100 mCrab source in a 6--8 hour observation. To achieve such high sensitivity, low energy response of the detector is important because the source count rate is generally dominated by the lowest energy photons. We have developed new PMT assemblies specifically designed for PoGO to read-out weak scintillation light of one photoelectron (1 p.e.) level. A beam test of a prototype detector array was conducted at the KEK Photon Factory, Tsukuba in Japan. The experimental data confirm that PoGO can detect polarization of 80-85 % polarized beam down to 30 keV with a modulation factor 0.25 +/- 0.05.

We propose a university-class micro-satellite "Hu-ring" to localize and study gamma-ray bursts. The primary mission of "Hu-ring" is to localize gamma-ray bursts with an 10 arcmin accuracy in real time, and transmit promptly the coordinates to the ground. Although many of its mission concepts are modeled after HETE-2, use of avalanche photodiodes (APDs), innovative photon detector device, make it possible to further reduce the size and the mass of the satellite. We designed "Hu-ring" within a size of 50 cm cube and a weight limit of 50 kg, so that it can be launched as a piggy-back payload of the Japanese H-IIA Launch Vehicle. The satellite is spin-stabilized, and has a half-sky field of view centered on the anti-sun direction. A set of scintillation counters equipped with rotation modulation collimators are employed for localization of GRBs. We also measure the soft/medium X-ray spectra of GRBs using APDs as a direct X-ray photon detectors. These two kinds of instruments cover the 0.5--200 keV energy range. The satellite bus is designed mostly with commercially available components in order to reduce the cost and the lead time. Following the HETE-2 model, in order to receive the prompt burst alerts it is designed to rely on a global network of receive-only low-cost ground stations, which may be hosted at research instutions with a small footprint. We performed analyses in many aspects: mechanical and thermal design of the satellite bus, attitude control simulations, power budget, ground contact schedule and downlink capacity, etc. We verified that the mission goal can be achieved with this proposed design philosophy.

The soft gamma-ray detector (SGD) on board NeXT (Japanese future high energy astrophysics mission) is a Compton telescope with narrow field of view (FOV), which utilizes Compton kinematics to enhance its background rejection capabilities. It is realized as a hybrid semiconductor gamma-ray detector which consists of silicon and CdTe (cadmium telluride) detectors. It can detect photons in a wide energy band (0.05-1 MeV) at a background level of 5 /spl times/ 10/sup -7/ counts/s/cm/sup 2//keV; the silicon layers are required to improve the performance at a lower energy band (