The Soft Gamma-ray Detector (SGD) is one of the instrument payloads onboard ASTRO-H, and will cover a wide energy band (60–600keV) at a background level 10 times better than instruments currently in ...orbit. The SGD achieves low background by combining a Compton camera scheme with a narrow field-of-view active shield. The Compton camera in the SGD is realized as a hybrid semiconductor detector system which consists of silicon and cadmium telluride (CdTe) sensors. The design of the SGD Compton camera has been finalized and the final prototype, which has the same configuration as the flight model, has been fabricated for performance evaluation. The Compton camera has overall dimensions of 12cm×12cm×12cm, consisting of 32 layers of Si pixel sensors and 8 layers of CdTe pixel sensors surrounded by 2 layers of CdTe pixel sensors. The detection efficiency of the Compton camera reaches about 15% and 3% for 100keV and 511keV gamma rays, respectively. The pixel pitch of the Si and CdTe sensors is 3.2mm, and the signals from all 13,312 pixels are processed by 208 ASICs developed for the SGD. Good energy resolution is afforded by semiconductor sensors and low noise ASICs, and the obtained energy resolutions with the prototype Si and CdTe pixel sensors are 1.0–2.0keV (FWHM) at 60keV and 1.6–2.5keV (FWHM) at 122keV, respectively. This results in good background rejection capability due to better constraints on Compton kinematics. Compton camera energy resolutions achieved with the final prototype are 6.3keV (FWHM) at 356keV and 10.5keV (FWHM) at 662keV, which satisfy the instrument requirements for the SGD Compton camera (better than 2%). Moreover, a low intrinsic background has been confirmed by the background measurement with the final prototype.
•The final prototype of the Si/CdTe Compton camera for the ASTRO-H SGD was completed.•The detailed design of the Compton camera is described.•The unprecedented high efficiency and high sensitivity are achieved.•The evaluation in the laboratory by using the prototype was performed.•The spectral performance, effective area and low background have been confirmed.
Long-term test of a stacked CdTe mini-HXI setup Maier, Daniel; Horeau, Benoit; Laurent, Philippe ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2018, Volume:
912
Journal Article
Peer reviewed
This work presents a long-term operation of two stacked CdTe double sided strip detectors that are comparable with the CdTe detectors onboard Hitomi’s HXI. The goal of this test is to study the ...evolution of the spectroscopic performance of the detectors during a one year operation cycle which resembles the in-orbit operation cycle of Hitomi HXI. Crystal defects inside CdTe cause a degradation of the spectroscopic performance (polarization effect) of the crystal which is becoming worse during detector operation. In order to prevent crystal polarization, the detectors are reset (switch-off of the depletion voltage) once a day. Our main investigation was to study if a long-term degradation can occur as a result of incomplete depolarization during the reset. We present the hardware setup and the analytical steps that were used to investigate the detector stability during each day and over the whole testing period. For the anode signals our results show at 60 keV: a daily line drift of (−2.8±0.7) eV/ks while the long-term drift is (−1.5±1.2) eV/day. The degradation of the energy resolution is measured to be (+2.4±0.3) eV/ks FWHM and the loss of efficiency is (−0.29±0.02) %/ks.
Aim
Although scales specific to resilience are available and widely used, qualities of resilience could be culturally sensitive. This study aimed to develop a concise scale of resilience for Japanese ...populations, and compare its validity to that of the Resilience Scale 14‐item version (RS‐14), one of the most widely used scales for measuring resilience.
Methods
The Tachikawa Resilience Scale (TRS) was developed on the basis of data obtained from unstructured interviews with Japanese motor vehicle accident survivors without psychiatric disorder. The reliability and validity of the TRS and RS‐14 were then examined in cross‐sectional studies performed with 523 company workers and 140 psychiatric outpatients.
Results
The TRS and RS‐14 were negatively correlated with depressive symptoms in company workers and psychiatric outpatients and with anxiety in psychiatric outpatients, and were positively correlated with social support in company workers. Internal consistency and test–retest reliability of the TRS were high. Construct validity of the TRS was equivalent to that of the RS‐14 in company workers, and higher than that of the RS‐14 in psychiatric outpatients.
Conclusion
The reliability and validity of the TRS and RS‐14 in Japanese company workers and patients with psychiatric disorders were acceptable. The validity of the TRS was equivalent to or better than that of the RS‐14. Although the TRS cannot be regarded as an established scale due to a lack of theoretical rationale, the results of this study suggest that scales measuring resilience that cover cultural aspects might be more relevant in given populations.
We have developed a new Compton camera based on silicon (Si) and cadmium telluride (CdTe) semiconductor double-sided strip detectors (DSDs). The camera consists of a 500-μm-thick Si-DSD and four ...layers of 750-μm-thick CdTe-DSDs all of which have common electrode configuration segmented into 128 strips on each side with pitches of 250μm. In order to realize high angular resolution and to reduce size of the detector system, a stack of DSDs with short stack pitches of 4mm is utilized to make the camera. Taking advantage of the excellent energy and position resolutions of the semiconductor devices, the camera achieves high angular resolutions of 4.5° at 356keV and 3.5° at 662keV. To obtain such high resolutions together with an acceptable detection efficiency, we demonstrate data reduction methods including energy calibration using Compton scattering continuum and depth sensing in the CdTe-DSD. We also discuss imaging capability of the camera and show simultaneous multi-energy imaging.
A front-end ASIC with spectroscopic capability was developed to construct a prototype CdTe pixel detector for future use in focusing hard X-ray telescopes. The ASIC is designed for a hybrid ...configuration, where each CdTe sensor pixel is vertically connected to a corresponding pixel cell fabricated in the readout ASIC. The readout chip consists of a 12 × 12 matrix of identical 270×270 μm 2 pixel cells, and was implemented with TSMC 0.35 μm CMOS technology. The low noise performance achieved an equivalent noise charge distribution of 50 ±10 e - . A CdTe pixel detector was mounted on the ASIC using an In/Au-stud bump-bonding technique. The detector was operated in self-trigger mode, and showed good spectral performance with energy resolution of 870 eV (FWHM) at 59.5 keV.
We have developed an integrated response generator based on Monte Carlo simulation for Compton cameras composed of silicon (Si) and cadmium telluride (CdTe) semiconductor detectors. In order to ...construct an accurate detector response function, the simulation is required to include a comprehensive treatment of the semiconductor detector devices and the data processing system in addition to simulating particle tracking. Although CdTe is an excellent semiconductor material for detection of soft gamma rays, its ineffective charge transport property distorts its spectral response. We investigated the response of CdTe pad detectors in the simulation and present our initial results here. We also performed the full simulation of prototypes of Si/CdTe semiconductor Compton cameras and report on the reproducibility of detection efficiencies and angular resolutions of the cameras, both of which are essential performance parameters of astrophysical instruments.
Schottky CdTe diode detectors suffer from a polarization phenomenon, which is characterized by degradation of the spectral properties over time following exposure to high bias voltage. This is ...considered attributable to charge accumulation at deep acceptor levels. A Schottky CdTe diode was illuminated with an infrared light for a certain period during a bias operation, and two opposite behaviors emerged. The detector showed a recovery when illuminated after the bias-induced polarization had completely progressed. Conversely, when the detector was illuminated before the emergence of bias-induced polarization, the degradation of the spectral properties was accelerated. Interpretation of these effects and discussion on the energy level of deep acceptors are presented.
We report on the recent development of a 32-channel low-noise analog front-end ASIC "KW03" for hard X-ray and gamma-ray detectors. The ASIC aims for the readout of strip or pixel (pad) detectors ...utilizing silicon and cadmium telluride (CdTe) as detector materials. Each readout channel includes a charge-sensitive amplifier, bandpass filters and a sample-and-hold circuit. It also includes a leakage current compensation and pole-zero cancellation circuits to meet the various detector requirements. The equivalent noise level of a typical channel reaches 89 e - @ 0 pF (rms) and shows an input-capacitance characteristic of 7.5 e - /pF between 0 pF and 10 pF with a power consumption of 3 mW per channel. We mounted the ASIC on a low-temperature co-fired ceramic (LTCC) package and evaluated the spectral performance by combining with a CdTe diode detector. As a result, the gamma-ray spectrum of radioactive source 241 Am was obtained with a good energy resolution of 2.23 keV (FWHM) for gamma rays of 59.5 keV at -20°C.
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