The Hard X-ray Detector (HXD) on board Suzaku covers a wide energy range from 10 keV to 600 keV by the combination of silicon PIN diodes and GSO scintillators. The HXD is designed to achieve an extremely low in-orbit background based on a combination of new techniques, including the concept of a well-type active shield counter. With an effective area of $142 \,\mathrm{cm}^{2}$ at 20 keV and $273 \,\mathrm{cm}^{2}$ at 150 keV, the background level at sea level reached $\sim 1 \times 10^{-5} \,\mathrm{cts} \,\mathrm{s}^{-1} \,\mathrm{cm}^{-2} \,\mathrm{keV}^{-1}$ at 30 keV for the PIN diodes, and $\sim 2 \times 10^{-5} \,\mathrm{cts} \,\mathrm{s}^{-1} \,\mathrm{cm}^{-2} \,\mathrm{keV}^{-1}$ at 100 keV, and $\sim 7 \times 10^{-6} \,\mathrm{cts} \,\mathrm{s}^{-1} \,\mathrm{cm}^{-2} \,\mathrm{keV}^{-1}$ at 200 keV for the phoswich counter. Tight active shielding of the HXD results in a large array of guard counters surrounding the main detector parts. These anti-coincidence counters, made of $\sim 4 \,\mathrm{cm}$ thick BGO crystals, have a large effective area for sub-MeV to MeV $\gamma$-rays. They work as an excellent $\gamma$-ray burst monitor with limited angular resolution ($\sim 5^{\circ}$). The on-board signal-processing system and the data transmitted to the ground are also described.

The in-orbit performance and calibration of the Hard X-ray Detector (HXD) on board the X-ray astronomy satellite Suzaku are described. Its basic performances, including a wide energy bandpass of 10–600 keV, energy resolutions of $\sim 4 \,\mathrm{keV}$ (FWHM) at 40 keV and $\sim 11\%$ at 511 keV, and a high background rejection efficiency, have been confirmed by extensive in-orbit calibrations. The long-term gains of PIN-Si diodes have been stable within 1% for half a year, and those of scintillators have decreased by 5–20%. The residual non-X-ray background of the HXD is the lowest among past non-imaging hard X-ray instruments in energy ranges of 15–70 and 150–500 keV. We provide accurate calibrations of energy responses, angular responses, timing accuracy of the HXD, and relative normalizations to the X-ray CCD cameras using multiple observations of the Crab Nebula.

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The nature of dark matter and properties of neutrinos are among the most pressing issues in contemporary particle physics. The dual-phase xenon time-projection chamber is the leading technology to cover the available parameter space for weakly interacting massive particles, while featuring extensive sensitivity to many alternative dark matter candidates. These detectors can also study neutrinos through neutrinoless double-beta decay and through a variety of astrophysical sources. A next-generation xenon-based detector will therefore be a true multi-purpose observatory to significantly advance particle physics, nuclear physics, astrophysics, solar physics, and cosmology. This review article presents the science cases for such a detector.

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 and a large effective area of 400 cm 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.

A : We report an in-situ measurement of the nuclear recoil (NR) scintillation decay time constant in liquid xenon (LXe) using the XMASS-I detector at the Kamioka underground laboratory in Japan. XMASS-I is a large single-phase LXe scintillation detector whose purpose is the direct detection of dark matter via NR which can be induced by collisions between Weakly Interacting Massive Particles (WIMPs) and a xenon nucleus. The inner detector volume contains 832 kg of LXe.252 Cf was used as an external neutron source for irradiating the detector. The scintillation decay time constant of the resulting neutron induced NR was evaluated by comparing the observed photon detection times with Monte Carlo simulations. Fits to the decay time prefer two decay time components, one for each of the Xe * 2 singlet and triplet states, with τ S = 4.3±0.6 ns taken from prior research, τ T was measured to be 26.9 +0.7 −1.1 ns with a singlet state fraction F S of 0.252 +0.027 −0.019 . We also evaluated the performance of pulse shape discrimination between NR and electron recoil (ER) with the aim of reducing the electromagnetic background in WIMP searches. For a 50% NR acceptance, the ER acceptance was 13.7±1.0% and 4.1±0.7% in the energy ranges of 5-10 keV ee and 10-15 keV ee , respectively.

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