Y. Kuramoto

Recent progress of avalanche photodiodes in high-resolution X-rays and γ-rays detection

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.

An active gain-control system for Avalanche photo-diodes under moderate temperature variations

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.

Development of Mono-Propellant Propulsion System for A Japanese Microsatellite "Hodoyoshi-1"

As the development of microsatellite is recently increasing in the world, miniaturization of elements for space use is strongly desired to make efficient use of microsatellite with respect to its dimensions, cost, and capability of space mission. As for propulsion, chemical propulsion is the most suitable to microsatellite with progress in miniaturization because of its high thrust density, short term injection, and easiness to handle. However, the conventional propulsion for satellite is difficult to handle the propellant, hydrazine, due to its toxicity and high cost, so that universities and non-governmental associations developing their microsatellites have not installed such propulsion so far. Accordingly, we have been developing a propulsion system for microsatellites based on Hydrogen Peroxide because of its little toxicity, low cost, and handling properties compared to the conventional propulsion system. Thus, we completed a mono-propellant propulsion system for microsatellite with the policies of SAFTY FIRST and EFFECTIVE COTS. Now we are planning to demonstrate our propulsion system in a Japanese microsatellite, Hodoyoshi-1, to execute its phase shift in orbit. The propulsion system has a mono-propellant thruster with 500mN of thrust and 80 seconds of specific impulse. We already evaluated its performance in injection tests on ground and in vacuum, and are planning to conduct the detailed vacuum test and mechanical environment test such as vibration test for its launch. In this paper, we present the innovative propulsion system and its injection test.

In-orbit performance of avalanche photodiode as radiation detector onboard a pico-satellite Cute-1.7+APD II

Cute-1.7+APD II is the third pico-satellite developed by students at the Tokyo Institute of Technology. One of the primary goals of the mission is to validate the use of avalanche photodiodes (APDs) as a radiation detector for the first time in a space experiment. The satellite was successfully launched by an ISRO PSLV-C9 rocket in Apr 2008 and has since been in operation for more than 20 months. Cute-1.7+APD II carries two reversetype APDs to monitor the distribution of low energy particles down to 9.2 keV trapped in a Low Earth Orbit (LEO), including South Atlantic Anomaly (SAA) as well as aurora bands. We present the design parameters and various preflight tests of the APDs prior to launch, particularly, the high counting response and active gain control system for the Cute-1.7+APD II mission. Examples of electron/proton distribution, obtained in continuous 12-hour observations, will be presented to demonstrate the initial flight performance of the APDs in orbit.