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The hard X-ray detector (HXD-II) is one of the three scientific instruments onboard Japanese X-ray astronomy satellite Astro-E2 scheduled to be launched in 2005. This mission is very unique in a point of having a lower background than any other past missions in the 10-600 keV range. In the HXD-II, the large and thick BGO crystals are used as active shields for particle and gamma-ray background to the main detector. They have a wide field of view of ~2[pi] and a large effective area of 400 [cm.sup.2] even at 1 MeV. Hence, the BGO shields have been developed as a wide-band all-sky monitor (WAM) with a broadband coverage of 50-5000 keV. In this paper, overall design and performance of the HXD-II/WAM based on the results of preflight calibration tests carried out in June 2004 are described. By irradiating various radio isotopes with the WAM flight model, we verified that it had comparable capabilities with other gamma-ray burst detectors. Index Terms--Astronomical satellites, hard X-ray detectors, scintillation detectors, X-ray astronomy.

The soft gamma-ray detector (SGD) onboard the Japanese future high energy astrophysics mission (NEXT) is a Compton telescope with narrow field of view, 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 cadmium telluride (CdTe) detectors. It can detect photons in a wide energy band (0.05-1 MeV) at a background level of 5 x [10.sup.-7] counts/s/[cm.sup.2]/keV; the silicon layers are required to improve the performance at a lower energy band ( Index Terms--Cadmium telluride (CdTe), Compton camera, gamma-ray astronomy detectors, polarimetry, silicon radiation detectors.

This paper summarizes the design and performance of the hard X-ray detector constructed for the ASTRO-E satellite. The detector utilizes the GSO/BGO well-type phoswich counters in a compound-eye configuration to achieve an extremely low background level of a few x [10.sup.-5] counts [s.sup.-1] [cm.sup.-2]ke[V.sup.-1] [1]. The GSO scintillators installed in the BGO active shield wells are sensitive to 30-600 keV photons, while the 2-mm-thick silicon PIN diodes, placed in front of each GSO crystal, cover the 10-60 keV energy band with a spectral resolution of ~3.5-keV full-width at half-maximum. The design goals, of both low background and high energy resolution, in the hard X-ray bands were verified through the preflight calibration experiments. Index Terms--ASTRO-E, background, hard X-ray detector, sensitivity, spectral response.

The ASTRO-E hard X-ray detector utilizes GSO([Gd.sub.2]Si[O.sub.5]: Ce 0.5% mol)--BGO([Bi.sub.4][Ge.sub.3][O.sub.12]) well-type phoswich counters [1] in compound-eye configuration to achieve an extremely low background level of about a few times [10.sup.-5] counts [s.sup.-1] [cm.sup.-2] ke[V.sup.-1]. The GSO scintillators placed at the bottom of the BGO well observe photons in the energy range 30-600 keV. To cover the lower energy range of 10-60 keV, silicon p-i-n diodes of 2 mm in thickness and 21.5x 21.5 [mm.sup.2] in size were newly developed and placed in front of the GSO scintillators. The p-i-n diode exhibits complex spectral responses, including subpeak and low energy tail components. To examine the origin of these components, we measured the spatially resolved response of the p-i-n diode and confirmed that the subpeak and the low energy tail are related to the electrode structures and electric fields in the p-i-n diode, respectively. Index Terms--ASTRO.E, hard X-ray detector, p-i-n silicon diode, spectral response.

Presents a study on the resolved response of p-i-n diode to determine the origin of ASTRO-E hard X-ray detector. Description of p-i-n diodes; Details of the experiment; Results and conclusion.