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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Proceedings of SPIE - The International Society for Optical Engineering 9144 2014年12月3日The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions developed by the Institute of Space and Astronautical Science (ISAS), with a planned launch in 2015. The ASTRO-H mission is equipped with a suite of sensitive instruments with the highest energy resolution ever achieved at E > 3 keV and a wide energy range spanning four decades in energy from soft X-rays to gamma-rays. The simultaneous broad band pass, coupled with the high spectral resolution of Delta E < 7 eV of the micro-calorimeter, will enable a wide variety of important science themes to be pursued. ASTRO-H is expected to provide breakthrough results in scientific areas as diverse as the large-scale structure of the Universe and its evolution, the behavior of matter in the gravitational strong field regime, the physical conditions in sites of cosmic-ray acceleration, and the distribution of dark matter in galaxy clusters at different redshifts.
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日本物理学会講演概要集 69(1) 129-129 2014年3月5日
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日本物理学会講演概要集 69(1) 128-128 2014年3月5日
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日本物理学会講演概要集 69(1) 129-129 2014年3月5日
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日本物理学会講演概要集 69(1) 128-128 2014年3月5日
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日本物理学会講演概要集 69(1) 129-129 2014年3月5日
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Proceedings of SPIE - The International Society for Optical Engineering 9144 2014年© 2014 SPIE. The Soft Gamma-ray Detector (SGD) is one of observational instruments onboard the ASTRO-H, and will provide 10 times better sensitivity in 60{600 keV than the past and current observatories. The SGD utilizes similar technologies to the Hard X-ray Imager (HXI) onboard the ASTRO-H. The SGD achieves low background by constraining gamma-ray events within a narrow field-of-view by Compton kinematics, in addition to the BGO active shield. In this paper, we will present the results of various tests using engineering models and also report the flight model production and evaluations.
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Proceedings of SPIE - The International Society for Optical Engineering 9144 2014年© 2014 SPIE. The hard X-ray imager (HXI) and soft gamma-ray detector (SGD) onboard Astro-H observe astronomical objects with high sensitivity in the hard X-ray (5-80 keV) and soft gamma-ray (40-600 keV) energy bands. To achieve this high sensitivity, background rejection is essential, and these detectors are surrounded by large and thick bismuth germinate scintillators as an active shield. We have developed adequate trigger logic for both the HXI and SGD to process signals from main detector and BGO shield simultaneously and then we optimized the trigger delay and width, with consideration of the trigger latch efficiency. The shield detector system performs well, even after it is assembled as the HXI sensor. The energy threshold maintains the same level as that observed during the prototype development phase, and the experimental room background level of the main detector is successfully reduced by our optimized trigger timing.
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Proceedings of SPIE - The International Society for Optical Engineering 9144 2014年© 2014 SPIE. The Soft Gamma-ray Detector (SGD) is a Si/CdTe Compton telescope surrounded by a thick BGO active shield and is scheduled to be onboard the ASTRO-H satellite when it is launched in 2015. The SGD covers the energy range from 40 to 600 keV with high sensitivity, which allows us to study nonthermal phenomena in the universe. The SGD uses a Compton camera with the narrow field-of-view (FOV) concept to reduce the non-Xray background (NXB) and improve the sensitivity. Since the SGD is essentially a nonimaging instrument, it also has to cope with the cosmic X-ray background (CXB) within the FOV. The SGD adopts passive shields called "fine collimators" (FCs) to restrict the FOV to ≤ 0.6° for low-energy photons (≤ 100 keV), which reduces contamination from CXB to less than what is expected due to NXB. Although the FC concept was already adopted by the Hard X-ray Detector onboard Suzaku, FCs for the SGD are about four times larger in size and are technically more difficult to operate. We developed FCs for the SGD and confirmed that the prototypes function as required by subjecting them to an X-ray test and environmental tests, such as vibration tests. We also developed an autocollimator system, which uses visible light to determine the transmittance and the optical axis, and calibrated it against data from the X-ray test. The acceptance tests of flight models started in December 2013: five out of six FCs were deemed acceptable, and one more unit is currently being produced. The activation properties were studied based on a proton-beam test and the results were used to estimate the in-orbit NXB.
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SPACE TELESCOPES AND INSTRUMENTATION 2014: ULTRAVIOLET TO GAMMA RAY 9144 2014年Recent progress in wide field of view or all-sky observations such as Swift/BAT hard X-ray monitor and Fermi GeV gamma-ray observatory has opened up a new era of time-domain high energy astro-physics addressing new insight in, e.g., particle acceleration in the universe. MeV coverage with comparable sensitivity, i.e. 1 similar to 10 mCrab is missing and a new MeV all-sky observatory is needed. These new MeV mission tend to be large, power-consuming and hence expensive, and its realization is yet to come. A compact sub-MeV (0.2-2 MeV) all-sky mission is proposed as a path finder for such mission. It is based on a Si/CdTe semiconductor Compton telescope technology employed in the soft gamma-ray detector onboard ASTRO-H, to be launched in to orbit on late 2015. The mission is kept as small as 0.5 x 0.5 x 0.4 m(3), 150 kg in weight and 200 W in power in place of the band coverage above a few MeV, in favor of early realization as a sub-payload to other large platforms, such as the international space station.
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Proceedings of SPIE - The International Society for Optical Engineering 9144 2014年© 2014 SPIE. The Hard X-ray Imager and the Soft Gamma-ray Detector, onboard the 6th Japanese X-ray satellite ASTRO-H, aim at unprecedentedly-sensitive observations in the 5-80 keV and 40-600 keV bands, respectively. Because their main sensors are composed of a number of semi-conductor devices, which need to be operated in a temperature of -20 to -15â-▪C, heat generated in the sensors must be efficiently transported outwards by thermal conduction. For this purpose, we performed thermal design, with the following three steps. First, we additionally included thermally-conductive parts, copper poles and graphite sheets. Second, constructing a thermal mathematical model of the sensors, we estimated temperature distributions in thermal equilibria. Since the model had rather large uncertainties in contact thermal conductions, an accurate thermal dummy was constructed as our final step. Vacuum measurement with the dummy successfully reduced the conductance uncertainties. With these steps, we confirmed that our thermal design of the main sensors satisfies the temperature requirement.
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日本物理学会講演概要集 68(2) 114-114 2013年8月26日
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日本物理学会誌 68(6) 382-386 2013年6月5日2011年3月に東北地方を襲った大地震によって福島第一原子力発電所から放出された放射性物質が,国民生活に大きな影響を与えており,効率の良い除染が我が国の喫緊の課題となっている.われわれは,次期X線衛星ASTRO-Hのために開発を行ってきたSi/CdTeコンプトンカメラの技術を応用し,超広角コンプトンカメラと呼ばれるガンマ線カメラを急遽作り上げた.現地において,放射性物質中の原子核が崩壊して安定な原子核になる過程で放出されるガンマ線のイメージング実験を行い,その源となっている放射性物質の分布を知ることができることを示した.
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日本物理学会講演概要集 68(1) 164-164 2013年3月26日
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日本物理学会講演概要集 68(1) 134-134 2013年3月26日
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映像情報メディア学会誌 : 映像情報メディア = The journal of the Institute of Image Information and Television Engineers 67(3) 197-201 2013年3月1日
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IEEE Nuclear Science Symposium Conference Record 2013年Imaging technique of RI tracer for physiological function analysis is substantially useful and popular as positron emission tomography (PET), positron-emitting tracer imaging system (PETIS) or single photon emission computed tomography (SPECT). Recently, Compton camera is thought to become a promising imaging apparatus in several field, for example, medical, biological application and security inspection, because of its simultaneous imaging ability against the wide energy range gamma-rays from a few hundred keV to a few MeV. In this work, three-dimensional imaging ability of our Compton camera system developed for human body imaging has been studied by use of Monte Carlo simulation. The imaging system consists of plural Compton-camera head-modules having the diameter of 20 cm and height of 20 cm. Each of head modules has a 32 mm wide Si double-side strip detector (DSD) and four CdTe-DSDs stacked at intervals of 4 mm. The head modules are settled on XYZ-stages and can be moved by XYZ-stage around the subject imaged during data acquisition. The simulation study was performed by use of a Geant4-based Compton-camera simulator developed by JAXA/ISAS. Three sphere-shaped gamma-sources, having diameters of 10, 13 and 17 mm, of the NEMA NU2-2007 standard body-phantom was assumed to be placed around the center of simulation space. The RI density is uniform and the energy of gamma ray 511 keV. Six camera-placements around the back and a side of the body phantom. Three-dimensional image was reconstructed by use of the List-Mode Expectation-Maximizing Maximum-Likelihood method. The positions of each sphere were clearly identified at the correct positions. The RI distributions of the imaging result are not asymmetrical between X- and Z-direction, which is found to be owing to the asymmetrical placement of the detector stacks. The RI intensities deduced from the image tend to reflect the real RI intensities although improvement is still required. © 2013 IEEE.
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IEEE Nuclear Science Symposium Conference Record 2013年We studied a new method to monitor a beam range in heavy-ion radiation therapy by measuring low energy photons emitted from a track of the ion beam. A 290 MeV/u carbon beam was injected into a cylindrical water phantom. A CdTe semiconductor detector with a lead slit having a width of 2mm was placed at a side of the phantom. In order to measure the position dependence of the low energy photon count, the beam range was varied by changing the injection energy using a binary energy degrader placed about 100 cm upstream of the beam focal point. The measured photon count decreased when the detector got closer to the end point of the beam range and the derivative of the photon count clearly changed in front of the range position. This was explained by our theoretical study assuming the photons were secondary electron bremsstrahlung. These results indicate that this new method could estimate the range position from the observation of bremsstrahlung with an accuracy of a few mm. © 2013 IEEE.
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O plus E : Optics + electronics 34(12) 1146-1149 2012年12月
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日本物理学会講演概要集 67(1) 31-31 2012年3月5日
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日本物理学会講演概要集 67(1) 139-139 2012年3月5日
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日本物理学会講演概要集 67(1) 138-138 2012年3月5日
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日本物理学会講演概要集 67(1) 138-138 2012年3月5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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日本学術振興会 科学研究費助成事業 新学術領域研究(研究領域提案型) 2018年6月 - 2023年3月
