Y. Tsubuku

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.

X-ray polarimetry small satellite TSUBAME

“TSUBAME” is a university‐built small satellite mission to measure polarization of hard X‐ray photons (30–100 keV) from Gamma‐ray bursts (GRBs) using azimuthal angle anisotropy of Compton‐scattered photons. Polarimetry in the hard X‐ray and soft γ‐ray band plays a crucial role in the understanding of high energy emission mechanisms and the distribution of magnetic fields and radiation fields. TSUBAME has two instruments: the Wide‐field Bust Monitor (WBM) and the Hard X‐ray Compton Polarimeter (HXCP). The WBM determines on board the direction of the burst occurrence with an accuracy of 10 degrees, then using a high speed attitude control device, the HXCP is pointed to the GRB within 10 seconds after the burst occurrence to promptly detect polarized X‐ray photons from the GRB.We present a TSUBAME mission overview, results of a Monte Carlo simulation of the X‐ray polarization measurement and the plans for the future of this mission.

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.

Development of the X-ray polarimetry small satellite "TSUBAME"

TSUBAME is a university‐built small satellite mission to measure polarization of hard X‐ray photons (30–100 keV) from gamma‐ray bursts using azimuthal angle anisotropy of Compton‐scattered photons. Polarimetry in the hard X‐ray and soft gamma‐ray band should play a crucial role in the understanding of high energy emission mechanisms and the distribution of magnetic fields and radiation fields. TSUBAME has two instruments: the Wide‐field Bust Monitor (WBM) and the Hard X‐ray Compton Polarimeter (HXCP). The WBM detects a burst and determines on board the direction of the burst occurrence with an accuracy of 10 degrees. The spacecraft is then slewed to the GRB in 15 seconds from the trigger using CMG, a high speed attitude control device. HXCP will measure the polarized X‐ray photons from the GRB while the spacecraft is slowly spinning around the bore sight. In this paper, we present an overview of the TSUBAME mission, its expected performance of X‐ray polarization measurement based on Monte Carlo simulation...