研究者業績
基本情報
- 所属
- 国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 宇宙物理学研究系 准教授
- 学位
- 博士(理学)(2004年3月 東京大学)
- 研究者番号
- 60446599
- ORCID ID
https://orcid.org/0000-0003-0441-7404- J-GLOBAL ID
- 202001021434500706
- researchmap会員ID
- R000012970
研究キーワード
6経歴
2-
2022年3月 - 現在
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2006年7月 - 2022年2月
学歴
3-
2001年4月 - 2004年3月
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1999年4月 - 2001年3月
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1995年4月 - 1999年3月
受賞
2主要な論文
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Publications of the Astronomical Society of Japan 70(6) 2018年10月1日 査読有り責任著者We present the results from the Hitomi Soft Gamma-ray Detector (SGD) observation of the Crab nebula. The main part of SGD is a Compton camera, which in addition to being a spectrometer, is capable of measuring polarization of gamma-ray photons. The Crab nebula is one of the brightest X-ray / gamma-ray sources on the sky, and, the only source from which polarized X-ray photons have been detected. SGD observed the Crab nebula during the initial test observation phase of Hitomi. We performed the data analysis of the SGD observation, the SGD background estimation and the SGD Monte Carlo simulations, and, successfully detected polarized gamma-ray emission from the Crab nebula with only about 5 ks exposure time. The obtained polarization fraction of the phase-integrated Crab emission (sum of pulsar and nebula emissions) is (22.1 $\pm$ 10.6)% and, the polarization angle is 110.7$^o$ + 13.2 / $-$13.0$^o$ in the energy range of 60--160 keV (The errors correspond to the 1 sigma deviation). The confidence level of the polarization detection was 99.3%. The polarization angle measured by SGD is about one sigma deviation with the projected spin axis of the pulsar, 124.0$^o$ $\pm$0.1$^o$.
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 765 192-201 2015年9月2日 査読有り筆頭著者責任著者The Soft Gamma-ray Detector (SGD) is one of the instrument payloads onboard ASTRO-H, and will cover a wide energy band (60--600 keV) 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 12 cm x 12 cm x 12 cm, 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 100 keV and 511 keV gamma rays, respectively. The pixel pitch of the Si and CdTe sensors is 3.2 mm, and the signals from all 13312 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--2.0 keV (FWHM) at 60 keV and 1.6--2.5 keV (FWHM) at 122 keV, 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 6.3 keV (FWHM) at 356 keV and 10.5 keV (FWHM) at 662 keV, respectively, 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.
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IEEE Transactions on Nuclear Science 56(3) 777-782 2008年11月4日 査読有り筆頭著者責任著者We developed CdTe double-sided strip detectors (DSDs or cross strip detectors) and evaluated their spectral and imaging performance for hard X-rays and gamma-rays. Though the double-sided strip configuration is suitable for imagers with a fine position resolution and a large detection area, CdTe diode DSDs with indium (In) anodes have yet to be realized due to the difficulty posed by the segmented In anodes. CdTe diode devices with aluminum (Al) anodes were recently established, followed by a CdTe device in which the Al anodes could be segmented into strips. We developed CdTe double-sided strip devices having Pt cathode strips and Al anode strips, and assembled prototype CdTe DSDs. These prototypes have a strip pitch of 400 micrometer. Signals from the strips are processed with analog ASICs (application specific integrated circuits). We have successfully performed gamma-ray imaging spectroscopy with a position resolution of 400 micrometer. Energy resolution of 1.8 keV (FWHM: full width at half maximum) was obtained at 59.54 keV. Moreover, the possibility of improved spectral performance by utilizing the energy information of both side strips was demonstrated. We designed and fabricated a new analog ASIC, VA32TA6, for the readout of semiconductor detectors, which is also suitable for DSDs. A new feature of the ASIC is its internal ADC function. We confirmed this function and good noise performance that reaches an equivalent noise charge of 110 e- under the condition of 3-4 pF input capacitance.
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Astrophysical Journal 651(1 I) 421-437 2006年7月3日 査読有り筆頭著者責任著者We present results from quantitative modeling and spectral analysis of the high mass X-ray binary Vela X-1 obtained with the Chandra HETGS. The spectra exhibit emission lines from H-like and He-like ions driven by photoionization, as well as fluorescent emission lines from several elements in lower charge states. In order to interpret and make full use of the high-quality data, we have developed a simulator, which calculates the ionization and thermal structure of a stellar wind photoionized by an X-ray source, and performs Monte Carlo simulations of X-ray photons propagating through the wind. The emergent spectra are then computed as a function of the viewing angle accurately accounting for photon transport in three dimensions including dynamics. From comparisons of the observed spectra with the simulation results, we are able to find the ionization structure and the geometrical distribution of material in Vela X-1 that can reproduce the observed spectral line intensities and continuum shapes at different orbital phases remarkably well. It is found that a large fraction of X-ray emission lines from highly ionized ions are formed in the region between the neutron star and the companion star. We also find that the fluorescent X-ray lines must be produced in at least three distinct regions --(1)the extended stellar wind, (2)reflection off the stellar photosphere, and (3)in a distribution of dense material partially covering and possibly trailing the neutron star, which may be associated with an accretion wake. Finally, from detailed analysis of the emission lines, we demonstrate that the stellar wind is affected by X-ray photoionization.
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IEEE Transactions on Nuclear Science 52(5 III) 2045-2051 2005年10月 査読有り筆頭著者責任著者We are developing a Compton camera based on Si and CdTe semiconductor imaging devices with high energy resolution. In this paper, results from the most recent prototype are reported. The Compton camera consists of six layered double-sided Si Strip detectors and CdTe pixel detectors, which are read out with low noise analog ASICs, VA32TAs. We obtained Compton reconstructed images and spectra of line gamma-rays from 122 keV to 662 keV. The energy resolution is 9.1 keV and 14 keV at 356 keV and 511 keV, respectively. © 2005 IEEE.
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Astrophysical Journal 597(1 II) 2003年9月12日 査読有り筆頭著者責任著者We report the detection of a fully-resolved, Compton-scattered emission line in the X-ray spectrum of the massive binary GX 301-2 obtained with the High Energy Transmission Grating Spectrometer onboard the Chandra X-ray Observatory. The iron K-alpha fluorescence line complex observed in this system consists of an intense narrow component centered at an energy of E = 6.40 keV and a redward shoulder that extends down to ~6.24 keV, which corresponds to an energy shift of a Compton back-scattered iron K-alpha photon. From detailed Monte Carlo simulations and comparisons with the observed spectra, we are able to directly constrain the physical properties of the scattering medium, including the electron temperature and column density, as well as an estimate for the metal abundance.
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IEEE Transactions on Nuclear Science 48(4 I) 950-959 2001年7月20日 査読有りCadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) have been regarded as promising semiconductor materials for hard X-ray and Gamma-ray detection. The high atomic number of the materials (Z_{Cd} =48, Z_{Te} =52) gives a high quantum efficiency in comparison with Si. The large band-gap energy (Eg ~ 1.5 eV) allows us to operate the detector at room temperature. However, a considerable amount of charge loss in these detectors produces a reduced energy resolution. This problem arises due to the low mobility and short lifetime of holes. Recently, significant improvements have been achieved to improve the spectral properties based on the advances in the production of crystals and in the design of electrodes. In this overview talk, we summarize (1) advantages and disadvantages of CdTe and CdZnTe semiconductor detectors and (2) technique for improving energy resolution and photopeak efficiencies. Applications of these imaging detectors in future hard X-ray and Gamma-ray astronomy missions are briefly discussed.
MISC
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IEEE Nuclear Science Symposium Conference Record 1540-1543 2008年We have developed a prototype Compton camera for in vivo imaging by using semiconductor imaging devices, which has been proved to be successful techniques for the observation of high-energy astrophysical phenomena. In this camera, double-sided Si strip detectors (DSSDs) serve as scatterers and pixelized CdTe detectors (pCdTe) serve as absorbers. Some Compton images were acquired with radioisotopes in a phantom, which reveal certain characteristics of the field of view this camera, and the distributions of efficiencies and spatial resolutions. In a rat study, the nuclides in the body were distinguished by their γ-ray energies, and the difference in the distributions of the nuclides could also be successfully observed. © 2008 IEEE.
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Proceedings of SPIE - The International Society for Optical Engineering 7021 2008年We have developed a Compton camera with a double-sided silicon strip detector (DSSD) for hard X-ray and gamma-ray observation. Using a DSSD as a scatter detector of the Compton camera, we achieved high angular resolution of 3.4° at 511 keV. Through the imaging of various samples such as two-dimentional array sources and a diffuse source, the wide field-of-view (~ 100°) and the high spatial resolution (at least 20 mm at a distance of 60 mm from the DSSD) of the camera were confirmed. Furthermore, using the List-Mode Maximum-Likelihood Expectation-Maximization method, the camera can resolve an interval of 3 mm at a distance of 30 mm from the DSSD.
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IEEE Nuclear Science Symposium Conference Record 4000-4002 2008年We have developed a prototype of Compton camera using Si/CdTe semiconductors for medical imaging. In the case where a Compton camera has a single head and therefore the detection area of the Compton camera is restricted to small region, position resolution of depth direction is expected to be low. To overcome this weakness, we propose multi-head Compton camera. In this work, we evaluated the position resolutions of single- and double-head Compton camera by using Monte Carlo simulation. Consequently, the position resolution is about 6 mm for double-head camera while the position resolution of depth direction is about 15 mm for single-head camera. These results indicate that the position resolution is improved and clear 3D-image is taken by using multi-head Compton camera. © 2008 IEEE.
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日本物理学会講演概要集 62(2) 109-109 2007年8月21日
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日本物理学会講演概要集 62(2) 106-106 2007年8月21日
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日本物理学会講演概要集 62(2) 109-109 2007年8月21日
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日本物理学会講演概要集 62(2) 107-107 2007年8月21日
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日本物理学会講演概要集 62(1) 95-95 2007年2月28日
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日本物理学会講演概要集 62(1) 100-100 2007年2月28日
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日本惑星科学会秋季講演会予稿集 2007 132-132 2007年月・惑星の起源や進化を解き明かす際、その元素組成・分布を明らかにすることは、最も基本的かつ重要な観測である。高精度ガンマ線分光計をローバーへ搭載することにより、細かな地形に応じた元素地図が取得できる。これを実現するために、我々は小型で高いエネルギー分解能を実現できるテルル化カドミウム半導体を用いたガンマ線検出器の開発を進めている。本発表では検出器の基礎的な特性と搭載機器の基礎設計について紹介する。
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IEEE Nuclear Science Symposium Conference Record 4 2526-2531 2007年We report in-flight status of the X-ray detectors on board the Suzaku observatory, the 5th X-ray astronomy satellite of Japan launched on July 10, 2005. Suzaku is equipped with two types of Instruments: one is the X-ray Imaging Spectrometers (XISs) and the other is Hard X-ray Detector (HXD). XIS utilizes the X-ray CCD camera in combination with the grazing-incidence X-ray telescope. HXD is a non-imaging, hybrid detector utilizing Si PIN diodes and GSO/BGO phoswich counters. Suzaku takes a low-earth, circular orbit with an altitude of 560 km and an inclination of 31 deg. This means that Suzaku goes through the south atlantic anomaly about 1/3 of its revolutions. This has a large impact on the in-flight performance of XIS and HXD, which is reported in detail in the present paper. © 2007 IEEE.
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Proceedings of SPIE - The International Society for Optical Engineering 6706 2007年A semiconductor Compton camera for a balloon borne experiment aiming at observation in high energy astrophysics is developed. The camera is based on the concept of the Si/CdTe semiconductor Compton Camera, which features high-energy and high-angular resolution in the energy range from several tens of keV to a few MeV. It consists of tightly packed double-sided silicon strip detectors (DSSDs) stacked in four layers, and a total of 32 CdTe pixel detectors surrounding them. The Compton reconstruction was successfully performed and gamma-ray images were obtained from 511 keV down to 59.5 keV. The Angular Resolution Measure (ARM) at 511 keV is ∼ 2.5 degrees, thanks to the high energy resolution in both the DSSD and CdTe parts.
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Proceedings of SPIE - The International Society for Optical Engineering 6706 2007年Double-sided silicon strip detector (DSSD) is a key component to construct the next generation Compton telescope for the high-sensitivity observation in the energy region from several hundred keV to MeV. The concept of Compton camera we consider is using DSSD for scatterer, and high-stopping CdTe pixel detector for absorber. As the scatterer, DSSD has advantages of smaller band gap, higher efficiency of scattering, smaller Doppler broadening, good response time, and smaller number of readout channels. We have developed and confirmed that 0.3 mm-thick DSSD has enough performance. As a next step, in order to obtain more efficiency of higher energy gamma-rays, we developed newly designed DSSD which increase in thickness to 0.5 mm. We measured the basic properties of 0.5 mm thick DSSD, in terms of leakage current, capacitances, and noise characteristics. They can be full-depleted around 200 V, and we obtained the energy resolution of 1.3 keV (FWHM) for 60 keV at -10°C from one p-side strip. We also set up the newly developed read-out system which is based on technology of operating ASICs on floating ground, and performed 64 ch read-out on one side.
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Proceedings of SPIE - The International Society for Optical Engineering 6706 2007年We developed Schottky CdTe detectors using Al as an anode electrode and measured their performances. We first fabricated monolithic detectors with four different thicknesses of 0.5, 0.75, 1.0, and 2.0 mm. An Al anode electrode was implemented with a guard-ring structure. For the 0.5 mm thick CdTe detector, an energy resolution of 1.2 keV (FWHM) at 122 keV was achieved at a temperature of -20°C and a bias voltage of 400 V. Using the same technology, we next developed 8×8 pixel CdTe detectors, again with the four different thicknesses. The Al anode electrode was pixelated and the Pt cathode was made as a single plate. Signals from all pixels were successfully obtained and an energy resolution of 1.3 keV and 1.9 keV (FWHM) for 59.5 keV and 122 keV gamma-rays, was achieved at a temperature of -20°C and a bias voltage of 400 V using the 0.5 mm thick CdTe detector. The energy resolution was nearly the same in each pixel.
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日本物理学会講演概要集 61(2) 75-75 2006年8月18日
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日本物理学会講演概要集 61(2) 77-77 2006年8月18日
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日本物理学会講演概要集 60(2) 37-37 2005年8月19日
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日本物理学会講演概要集 60(2) 41-41 2005年8月19日
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日本物理学会講演概要集 60(2) 15-15 2005年8月19日
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NUOVO CIMENTO DELLA SOCIETA ITALIANA DI FISICA C-COLLOQUIA ON PHYSICS 28(4-5) 821-824 2005年7月The Hard X-ray Detector (HXD-II) is one of the three instruments onboard the Astro-E2 satellite scheduled for launch in 2005. The HXD-II consists of 16 main counters (Well units), surrounded by 20 active shield counters (Anti units). The Anti units have a large geometrical area of similar to 800 cm(2) with an uncollimated field of view covering similar to 2 pi steradian. Utilizing 2.6 cm thick BGO crystals: they realize a large effective area of 400 cm(2) for 1 MeV photons. In the energy range of 300-5000 keV, the expected effective area is significantly larger than those of other gamma-ray burst instruments, such as CGRO/BATSE, HETE-2/FREGATE, and GLAST/GBM. Therefore. the Anti units act as a Wideband All-sky, Monitor (WAM) for gamma-ray bursts in the energy range of 50-5000 keV.
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日本物理学会講演概要集 60(1) 197-197 2005年3月4日
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Proceedings of SPIE - The International Society for Optical Engineering 5501 229-240 2004年10月4日We are developing a Compton telescope based on high resolution Si and CdTe imaging devices in order to obtain a high sensitivity astrophysical observation in sub-MeV gamma-ray region. In this paper, recent results from the prototype Si/CdTe semiconductor Compton telescope are reported. The Compton telescope consists of a double-sided Si strip detector (DSSD) and CdTe pixel detectors, combined with low noise analog LSI, VA32TA. With this detector, we obtained Compton reconstructed images and spectra from line gamma-rays ranging from 81 keV up to 356 keV. The energy resolution is 3.8 keV and 7.9 keV at 122 keV and 356 keV, respectively, and the angular resolution is 9.9 degrees and 5.7 degrees at 122 keV and 356 keV, respectively.
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日本物理学会講演概要集 59(2) 63-63 2004年8月25日
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Proceedings of SPIE - The International Society for Optical Engineering 5198 209-216 2004年The properties of 32k CdZnTe detectors have been studied in the pre-flight calibration of Burst Alert Telescope (BAT) on-board the Swift Gamma-ray Burst Explorer (scheduled for launch in January 2004). After corrections of the linearity and the gain, the energy resolution of summed spectrum is 7.0 keV (FWHM) at 122 keV. In order to construct response matrices for the BAT instrument, we extracted mobility-lifetime (μτ) products for electrons and holes in the CdZnTe. Based on a new method applied to 57Co spectra taken at different bias voltages, μτ for electrons ranges from 5.0×10-4 to 1.0×10-2cm2V -1, while μτ for holes ranges from 1.0 × 10-5 to 1.7 × 10-4cm2V-1. We show that the distortion of the spectrum and the peak efficiency of the BAT instrument are well reproduced by the μτ database constructed in the calibration.
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Proceedings of SPIE - The International Society for Optical Engineering 5165 190-200 2004年In addition to providing the initial gamma-ray burst trigger and location, the Swift Burst Alert Telescope (BAT) will also perform an all-sky hard x-ray survey based on serendipitous pointings resulting from the study of gamma-ray bursts. BAT was designed with a very wide field-of-view (FOV) so that it can observe roughly 1/7 of the sky at any time. Since gamma-ray bursts are uniformly distributed over the sky, the final BAT survey coverage is expected to be nearly uniform. BAT's large effective area and long sky exposures will produce a 15 - 150 keV survey with up to 30 times better sensitivity than any previous hard x-ray survey (e.g. HEAO A4). Since the sensitivity of deep exposures in this energy range is systematics limited, the ultimate survey sensitivity depends on the relative sizes of the statistical and systematic errors in the data. Many careful calibration experiments were performed at NASA/Goddard Space Flight Center to better understand the BAT instrument's response to 15-150 keV gamma-rays incident from any direction within the FOV. Using radioactive sources of gamma-rays with known locations and energies, the Swift team can identify potential systematic errors in the telescope's performance and estimate the actual Swift hard x-ray survey sensitivity in flight. These calibration results will be discussed and a preliminary parameterization of the BAT instrument response will be presented. While the details of the individual BAT CZT detector response will be presented elsewhere in these proceedings, this talk will focus on the translation of the calibration experimental data into overall hard x-ray survey sensitivity.
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IEEE Nuclear Science Symposium Conference Record 1 309-313 2004年The Hard X-ray Detector (HXD) is one of the three instruments onboard Japanese X-ray astronomy satellite Astro-E2 scheduled for launch in 2005. This mission is very unique in a point of having a lower detector background than any other past missions in the 10-600 keV range. In the HXD, the large and thick BGO crystal are used as active shields for reducing the particle and gamma-ray background to the main detector. These anticoincidence shields are called as "Anti counters", which have a large geometrical area ∼ 800 cm 2 and an uncollimated field of view of ∼ 2π. Furthemore, they also have a larger effective area, corresponding to 400 cm2 at even 1 MeV due to their thick high-Z materials. This feature enables us to observe the high energy radiation of Gamma-ray bursts with a higher sensitivity than previous all-sky monitors. Hence, the Anti counters have been developed as all-sky monitors with a broadband coverage of 50-5000 keV. In this paper, we will describe overall design of the HXD Anti counters, then report on the results of the pre-flight calibration test on June 2004 using the flight model. By irradiating various radio isotopes with Anti counters, we confirmed that they have capability as all-sky monitors. It is striking that the low energy threshold has been archived about 30 keV in spite of large volume of BGO scintillators. © 2004 IEEE.
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IEEE Nuclear Science Symposium Conference Record 1 314-321 2004年The Soft Gamma-ray Detector (SGD) on board NeXT (Japanese future high energy astrophysics mission) is a Compton telescope with narrow field of view (FOV), 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 CdTe (Cadmium Telluride) detectors. It can detect photons in a wide energy band (0.05-1 MeV) at a background level of 5 × 10 -7 counts/s/cm 2/keV; the silicon layers are required to improve the performance at a lower energy band (<0.3 MeV). Excellent energy resolution is the key feature of the SGD, allowing to achieve both high angular resolution and good background rejection capability. An additional capability of the SGD, its ability to measure gamma-ray polarization opens up a new window to study properties of astronomical objects. We will present the development of key technologies to realize the SGD; high quality CdTe, low noise front-end ASIC and bump bonding tecnology. Energy resolutions of 1.7 keV (FWHM) for CdTe pixel detectors and 1.1 keV for Si strip detectors have been measured. We also present the validation of MC simulation used to evaluate the performance of the SGD. © 2004 IEEE.
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IEEE Nuclear Science Symposium Conference Record 7 4286-4290 2004年We are developing a Compton camera based on Si and CdTe semiconductor imaging devices with high energy resolution. In this paper, results from the most recent prototype are reported. The Compton camera consists of six stacked double-sided Si Strip detectors and CdTe pixel detectors, which are read out with low noise analog ASICs, VA32TAs. We obtained Compton reconstructed images and spectra of line gamma-rays from 80 keV to 662 keV. The energy resolution (FWHM) is 10 keV and 16 keV at 356 keV and 511 keV, respectively. © 2004 IEEE.
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IEEE Nuclear Science Symposium Conference Record 4 2174-2177 2004年We constructed a Monte-Carlo simulator framework for the radiation environment of Astro-E2, the Japanese 5th X-ray astronomy satellite. We used Geant4 as the simulator engine, and embedded it into the analysis framework derived from what has been used for other Astro-E2 software development. The entire architecture is designed to make the learning cost of the framework programming as low as possible for not only end users but developers, and we implemented some software mechanisms to register Geant4 components such as physics processes and geometry builder into the framework without using the Geant4's run manager explicitly. © 2004 IEEE.
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