Development of high performance Avalanche Photodiodes and dedicated analog systems for HXI/SGD detectors onboard the Astro-H mission

The Hard X-ray Imager (HXI) onboard Hitomi (ASTRO-H) is an imaging spectrometer covering hard xray energies of 5 to 80 keV. Combined with the Hard X-ray Telescope, it enables imaging spectroscopy with an angular resolution of 1 0 .7 half-power diameter, in a field of view of 9 0 × 9 0 . The main imager is composed of four layers of Si detectors and one layer of CdTe detector, stacked to cover a wide energy band up to 80 keV, surrounded by an active shield made of Bi 4 Ge 3 O 12 scintillator to reduce the background. The HXI started observations 12 days before the Hitomi loss and successfully obtained data from G21.5-0.9, Crab, and blank sky. Utilizing these data, we calibrate the detector response and study properties of in-orbit background. The observed Crab spectra agree well with a powerlaw model convolved with the detector response, within 5% accuracy. We find that albedo electrons in specified orbit strongly affect the background of the Si top layer and establish a screening method to reduce it. The background level over the full field of view after all the processing and screening is as low as the preflight requirement of 1 − 3 × 10 −4 counts s −1 cm −2 keV −1 . © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Section: Introductionmentioning

confidence: 99%

In-orbit performance and calibration of the Hard X-ray Imager onboard Hitomi (ASTRO-H)

2018

“…3, HXI-S consists of the HXI camera part and the active shield part. The former includes four layers of DSSDs and a CdTe-DSD imagers, whereas the latter is composed of nine active shield units made of large Bi 4 Ge 3 O 12 (BGO) scintillator crystals individually coupled to avalanche photo diodes (APD), 13 and the housing structure made of carbon-fiber-reinforced plastic (CFRP) to mechanically hold them. The DSSD and APD are purchased from Hamamatsu Photonics, the CdTe-DSD is from Acrorad, and the BGO is from Nikolaev Institute of Inorganic Chemistry.…”

Section: Overviewmentioning

confidence: 99%

Hard x-ray imager onboard Hitomi (ASTRO-H)

Nakazawa

Sato

Kokubun

et al. 2018

Abstract. The hard x-ray imaging spectroscopy system of "Hitomi" x-ray observatory is composed of two sets of hard x-ray imagers (HXI) coupled with hard x-ray telescopes (HXT). With a 12-m focal length, the system provides fine (1 0 :7 half-power diameter) imaging spectroscopy covering about 5 to 80 keV. The HXI sensor consists of a camera, which is composed of four layers of Si and one layer of CdTe semiconductor imagers, and an active shield composed of nine Bi 4 Ge 3 O 12 scintillators to provide low background. The two HXIs started observation on March 8 and 14, 2016 and were operational until 26 March. Using a Crab observation, 5 to 80 keV energy coverage and good detection efficiency were confirmed. The detector background level of 1 to 3 × 10 −4 counts s −1 keV −1 cm −2 (in detector geometrical area) at 5 to 80 keV was achieved, by cutting the high-background time-intervals, adopting sophisticated energy-dependent imager layer selection, and baffling of the cosmic x-ray background and active-shielding. This level is among the lowest of detectors working in this energy band. By comparing the effective area and the background, it was shown that the HXI had a sensitivity that is same to that of NuSTAR for point sources and 3 to 4 times better for largely extended diffuse sources. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

“…[52][53][54][55] The BGO crystal is dense (7.1 g∕cm 3 ), has a high stopping power (i.e., short radiation length of 1.1 cm), high optical transparency, and ability to form a large crystal although its light output is lower than NaI or CsI.…”

Section: Bgo Active Shield and Support Structurementioning

confidence: 99%

Design and performance of Soft Gamma-ray Detector onboard the Hitomi (ASTRO-H) satellite

Tajima

Watanabe

Fukazawa

et al. 2018

Abstract. Hitomi (ASTRO-H) was the sixth Japanese x-ray satellite that carried instruments with exquisite energy resolution of <7 eV and broad energy coverage of 0.3 to 600 keV. The Soft Gamma-ray Detector (SGD) was the Hitomi instrument that observed the highest energy band (60 to 600 keV). The SGD design achieves a low background level by combining active shields and Compton cameras where Compton kinematics is utilized to reject backgrounds coming from outside of the field of view. A compact and highly efficient Compton camera is realized using a combination of silicon and cadmium telluride semiconductor sensors with a good energy resolution. Compton kinematics also carries information for gamma-ray polarization, making the SGD an excellent polarimeter. Following several years of development, the satellite was successfully launched on February 17, 2016. After proper functionality of the SGD components were verified, the nominal observation mode was initiated on March 24, 2016. The SGD observed the Crab Nebula for approximately two hours before the spacecraft ceased to function on March 26, 2016. We present concepts of the SGD design followed by detailed description of the instrument and its performance measured on ground and in orbit. © The Authors.Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.