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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日本物理学会講演概要集 66(2) 113-113 2011年8月24日
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日本物理学会講演概要集 66(1) 122-122 2011年3月3日
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日本物理学会講演概要集 66(1) 122-122 2011年3月3日
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日本物理学会講演概要集 66(1) 123-123 2011年3月3日
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日本物理学会講演概要集 66(1) 122-122 2011年3月3日
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日本物理学会講演概要集 66(1) 123-123 2011年3月3日
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日本物理学会講演概要集 66(1) 33-33 2011年3月3日
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日本物理学会講演概要集 66(1) 34-34 2011年3月3日
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日本物理学会講演概要集 65(2) 81-81 2010年8月18日
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日本物理学会講演概要集 65(2) 82-82 2010年8月18日
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日本物理学会講演概要集 65(2) 17-17 2010年8月18日
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日本物理学会講演概要集 65(1) 107-107 2010年3月1日
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日本物理学会講演概要集 65(1) 103-103 2010年3月1日
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IEEE Nuclear Science Symposium Conference Record 1491-1493 2010年In this paper, we report the estimations of the lower detection limits of gamma ray energy for a newly developed Compton camera for applications to nuclear medicine imaging. We performed simulation studies to investigate the relationship of the distance between the scatterer and absorber detectors with the lower detection limit. In addition, imaging tests were performed by using multiple sources. © 2010 IEEE.
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IEEE Nuclear Science Symposium Conference Record 2004-2007 2010年In this study, the counting rate performance of a newly developed Compton camera for biological and medical applications was investigated; further, the sensitivity profile of this highly complicated imaging system was measured using 22Na and 18F point gamma-ray sources. 22Na was used to assess the imaging ability of this camera against the point source, and the intense 18F point source of 200 MBq was used to measure the sensitivity profiles of this camera for a range of counting rates over a short period. © 2010 IEEE.
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IEEE Nuclear Science Symposium Conference Record 3907-3909 2010年We have developed a prototype Cadmium Telluride pixel detector (SP8-01) to study its performance for high energy X-ray application requirement. The pixel format is 16 16 with the pitch of 200 m 200 m. The sensor thickness is 500m and the readout ASIC contains a charge sensitive amplifier, a shaper, upper and lower discriminators and a 20 bit counter in one cell. The SP8-01 detector achieved a required wide energy dynamic range from 15 to 120 keV with an Al Schottky sensor. © 2010 IEEE.
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Proceedings of SPIE - The International Society for Optical Engineering 7732 2010年The Hard X-ray Imager (HXI) is one of four detectors on board the ASTRO-H mission (6th Japanese X-ray satellite), which is scheduled to be launched in 2014. Using the hybrid structure composed of double-sided silicon strip detectors and a cadmium telluride double-sided strip detector, the instrument fully covers the energy range of photons collected with the hard X-ray telescope up to 80 keV with a high quantum efficiency. High spatial resolution of 250 μm and an energy resolution of 1-2 keV (FWHM) are both achieved with low noise front-end ASICs. In addition, the thick BGO active shields surrounding the main detector package is a heritage of the successful performance of the Hard X-ray Detector on board the Suzaku satellite. This feature enables the instrument to achieve an extremely high background reduction caused by cosmic-ray particles, cosmic X-ray background, and in-orbit radiation activation. In this paper, we present the detector concept, design, latest results of the detector development, and the current status of the hardware. © 2010 SPIE.
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IEEE Nuclear Science Symposium Conference Record 2140-2144 2009年The Soft Gamma-ray Detector (SGD) on board ASTRO-H (Japanese next high-energy astrophysics mission) 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 detector system which consists of silicon and CdTe (cadmium telluride) detectors. It can detect photons in a wide energy band (50-600 keV) at a background level 10 times better than that of the Suzaku Hard X-ray Detector, and is complimentary to the Hard X-ray Imager on board ASTRO-H with an energy coverage of 5-80 keV. Excellent energy resolution is the key feature of the SGD, allowing it to achieve good background rejection capability taking advantage of good angular resolution. An additional capability of the SGD, its ability to measure gamma-ray polarization, opens up a new window to study properties of gamma-ray emission processes. Here we describe the instrument design of the SGD, its expected performance, and its development status. ©2009 IEEE.
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IEEE Nuclear Science Symposium Conference Record 454-458 2009年The Focusing Optics X-ray Solar Imager (FOXSI) is a NASA sounding rocket mission which will study particle acceleration and coronal heating on the Sun through unprecedented high-resolution imaging in the hard X-ray energy band (5-15 keV). Energy release occurring in the quiet region of the Sun may potentially play an important role in the coronal heating mechanism. With a combination of high-resolution focusing Xray optics and fine-pitch imaging sensors, FOXSI will achieve superior sensitivity; two orders of magnitude better than that of the RHESSI satellite. FOXSI requires the spectral capability down to 5 keV, which requires a development of a new ASIC and detector with a better energy resolution. We plan to use a Doublesided Si Strip Detector (DSSD) with a low-noise front-end ASIC as the FOXSI focal plane detector, which will fulfill the scientific requirements on the spatial resolution, energy resolution, lower threshold energy and time resolution. We have designed and fabricated a DSSD with a thickness of 500 μm and a dimension of 9.6 mmx9.6 mm, containing 128 strips separated by a pitch of 75 μm, which corresponds to 8 arcsec at the focal length of 2 m. The DSSD was successfully operated in a laboratory experiment. Under a temperature of 20 °C and a bias voltage of 250 V, we obtained spectra from both sides of the electrodes. The energy resolution was measured to be 980 eV and 2.4 keV for the pside and n-side at 14 keV gamma-ray, sufficient for the FOXSI mission requirement. ©2009 IEEE.
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IEEE Nuclear Science Symposium Conference Record 4001-4003 2009年The next generation of Compton Camera based on Si and CdTe semiconductor has been developed in Japan for cosmic gamma-ray observation in space. Angular resolution and hence sensitivity of Compton Cameras are improved by employing the imaging semiconductors with good energy and spatial resolution. Moreover, for the energy range from several tens keV to a few MeV, silicon is suitable for the scattering part of the Compton camera since Compton cross-section is relatively large in Si, compared with the photo absorption cross section. Also effects of Doppler broadening is small. On the other hand, CdTe is suitable for the absorbers because of its high photo-absorption efficiency for gamma rays in this energy region. The high angular resolution and high energy resolution of the Si/CdTe Compton camera is very attractive features for medical applications. In the previous simulation study, we reported that the Compton camera has a low spatial resolution along the longitudinal direction, but it can be inproved by using two camera heads. In the present work, we measured the spatial resolution of the Compton camera, especially for the longitudinal direction. The spatial resolutions are compared with the simulation study. The longitudinal resolution is measured to be about 27 mm and the lateral one is about 5 mm at the distance of 6 cm from the surface of the top detector. The simulation result and the experimental one agree well with each other. Moreover we demonstrate the capability of three-dimensional imaging by using multi-head system consisted of plural Compton cameras. The spatial resolutions are consistent with the simulation result. These results implies that clear 3D-image can be realized by using a multi-head system of Compton cameras. ©2009 IEEE.
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Proceedings of SPIE - The International Society for Optical Engineering 7435 2009年We are developing imaging Cadmium Telluride (CdTe) pixel detectors optimized for astrophysical hard X-ray applications. Our hybrid detector consist of a CdTe crystal 1mm thick and 2cm × 2cm in area with segmented anode contacts directly bonded to a custom low-noise application specific integrated circuit (ASIC). The CdTe sensor, fabricated by ACRORAD (Okinawa, Japan), has Schottky blocking contacts on a 605 micron pitch in a 32 × 32 array, providing low leakage current and enabling readout of the anode side. The detector is bonded using epoxy-gold stud interconnects to a custom low noise, low power ASIC circuit developed by Caltech's Space Radiation Laboratory. We have achieved very good energy resolution over a wide energy range (0.62keV FWHM @ 60keV, 10.8keV FWHM @ 662keV). We observe polarization effects at room temperature, but they are suppressed if we operate the detector at or below 0°C degree. These detectors have potential application for future missions such as the International X-ray Observatory (IXO). © 2009 Copyright SPIE - The International Society for Optical Engineering.
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Proceedings of SPIE - The International Society for Optical Engineering 7437 2009年The Focusing Optics x-ray Solar Imager (FOXSI) is a sounding rocket payload funded under the NASA Low Cost Access to Space program to test hard x-ray focusing optics and position-sensitive solid state detectors for solar observations. Today's leading solar hard x-ray instrument, the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) provides excellent spatial (2 arcseconds) and spectral (1 keV) resolution. Yet, due to its use of indirect imaging, the derived images have a low dynamic range (<30) and sensitivity. These limitations make it difficult to study faint x-ray sources in the solar corona which are crucial for understanding the solar flare acceleration process. Grazing-incidence x-ray focusing optics combined with position-sensitive solid state detectors can overcome both of these limitations enabling the next breakthrough in understanding particle acceleration in solar flares. The FOXSI project is led by the Space Science Laboratory at the University of California. The NASA Marshall Space Flight Center, with experience from the HERO balloon project, is responsible for the grazing-incidence optics, while the Astro H team (JAXA/ISAS) will provide double-sided silicon strip detectors. FOXSI will be a pathfinder for the next generation of solar hard x-ray spectroscopic imagers. Such observatories will be able to image the non-thermal electrons within the solar flare acceleration region, trace their paths through the corona, and provide essential quantitative measurements such as energy spectra, density, and energy content in accelerated electrons.© 2009 SPIE.
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日本物理学会講演概要集 63(2) 69-69 2008年8月25日
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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
講演・口頭発表等
93共同研究・競争的資金等の研究課題
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