Publishing type：Research paper (scientific journal)  

© 2018 Elsevier B.V. FOXSI-3 (Focusing Optics X-ray Solar Imager) is an international sounding rocket experiment to observe hard X-rays from the Sun. The previous two flights successfully demonstrated the efficacy of the concept of direct solar imaging in hard X-ray band. For the third launch scheduled in the summer of 2018, we have fabricated a prototype of the CdTe Double-sided Strip Detector. To evaluate the basic performance, laboratory tests were conducted. Energy resolution (FWHM) of 0.8 keV at 13.9 keV and 1.3 keV at 59.5 keV are confirmed. Since the optic angular resolution is finer than the strip pitch of the detector at the focal plane, sub-strip position determination is important to make full use of the high precision of the optic. To test the possibility of sub-strip resolution, we developed a new method of investigating the detector strips with a fine multi-pinhole collimator. The results of the analysis were highly favorable and we confirmed the sub-strip resolution by making sub-strip images of multi-pinholes and flat-irradiation. The spectral uniformity over the detector is also confirmed using the sub-strip image of flat-irradiation.

DOI： 10.1016/j.nima.2018.07.011

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Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.3847/1538-4357/aad380

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Publishing type：Research paper (scientific journal)  

DOI： 10.1038/s41550-017-0269-z

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Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.3847/1538-4357/aa862e

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We present new constraints on the high-temperature emission measure of a non-flaring solar active region using observations from the recently flown Focusing Optics X-ray Solar Imager (FOXSI) sounding rocket payload. FOXSI has performed the first focused hard X-ray (HXR) observation of the Sun in its first successful flight on 2012 November 2. Focusing optics, combined with small strip detectors, enable high-sensitivity observations with respect to previous indirect imagers. This capability, along with the sensitivity of the HXR regime to high-temperature emission, offers the potential to better characterize high-temperature plasma in the corona as predicted by nanoflare heating models. We present a joint analysis of the differential emission measure (DEM) of active region 11602 using coordinated observations by FOXSI, Hinode/XRT, and Hinode/EIS. The Hinode-derived DEM predicts significant emission measure between 1MK and 3MK, with a peak in the DEM predicted at 2.0-2.5MK. The combined XRT and EIS DEM also shows emission from a smaller population of plasma above 8MK. This is contradicted by FOXSI observations that significantly constrain emission above 8 MK. This suggests that the Hinode DEM analysis has larger uncertainties at higher temperatures and that > 8MK plasma above an emission measure of 3 x 10(44) cm(-3) is excluded in this active region.

DOI： 10.1093/pasj/psu090

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

By using a new Compton camera consisting of a silicon double-sided strip detector (Si-DSD) and a CdTe double-sided strip detector (CdTe-DSD), originally developed for the ASTRO-H satellite mission, an experiment involving imaging radioisotopes was conducted to study their feasibility for hotspot monitoring. In addition to the hotspot imaging already provided by commercial imaging systems, identification of various radioisotopes is possible thanks to the good energy resolution obtained by the semiconductor detectors. Three radioisotopes of Ba-133 (356 keV), Na-22 (511 keV) and Cs-137 (662 keV) were individually imaged by applying event selection in the energy window and the gamma-ray images were correctly overlapped by an optical picture. Detection efficiency of 1.68 x10(-4) (effective area : 1.7 x10(-3) cm(2)) and angular resolution of 3.8 degrees were obtained by stacking five detector modules for a 662 keV gamma ray. The higher detection efficiency required in specific use can be achieved by stacking more detector modules. (C) 2012 Published by Elsevier B.V. Selection and/or peer review under responsibility of the organizing committee for TIPP 11.

DOI： 10.1016/j.phpro.2012.04.096

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

By reading out both anode and cathode strips, double-sided CdTe strip detectors can achieve a large area and a high position resolution with few readout channels, which makes them very attractive for X-ray and gamma-ray imaging and spectroscopy. We have developed double-sided CdTe strip detectors, 1.28 x 1.28 cm(2) in size and 0.5 and 2.0 mm in thickness. Both electrodes are divided into 32 orthogonal strips with a pitch of 400 gm. For a detector of 0.5 mm thickness, the energy resolution was measured to be 1.5 keV (FWHM) at 60 keV. For the 2.0-mm-thick detector, an energy resolution of 8.0 key (FWHM) at 662 key was obtained using only the anode signal. By combining both the anode and cathode signals, we successfully improved the spectral performance and measured an energy resolution of 5.9 keV (FWHM) at 662 key. (C) 2010 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.49.116702

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

A Compton camera has been developed based on Si and CdTe semiconductor detectors with high spatial and spectral resolution for hard X- and gamma-ray astrophysics applications. A semiconductor Compton camera is also an excellent polarimeter due to its capability to precisely measure the Compton scattering azimuth angle, which is modulated by linear polarization. We assembled a prototype Compton camera and conducted a beam test using nearly 100% linearly polarized gamma-rays at SPring-8. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nima.2010.07.077

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

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.

DOI： 10.1117/12.827950

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

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 (similar to 100 degrees) 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 ail interval of 3 mm at a distance of 30 mm from the DSSD.

DOI： 10.1117/12.788784

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

A Compton telescope with high angular resolution and high energy resolution is a promising detector for the next generation of astrophysics space missions aiming at hard X-rays and sub-MeV/MeV gamma-rays. We have been working on a semiconductor Compton camera based on silicon and cadmium telluride (Si/CdTe Compton telescope). The soft gamma-ray detector (SGD) employs a Si/CdTe Compton camera combined with a well-type active shield. It will be mounted on the NeXT mission, proposed to be launched around 2012. One Compton camera module in the SGD will consist of 24 layers of double-sided silicon strip detectors and four layers of CdTe pixel detectors. We carried out Monte Carlo simulations to investigate the basic performance of the detector. Design parameters of devices required in the simulation, such as energy resolution and position resolution of the detector, are based on the results from our prototype detector. From the simulation using current design parameters, the detection efficiency is found to be higher than 10% at similar to 100keV and the angular resolution to be 9 degrees and 4.4 degrees at 120keV and 330keV, respectively. The effects of changing the design parameters are also discussed. (c) 2007 Published by Elsevier B.V.

DOI： 10.1016/j.nima.2007.05.293

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Si and CdTe semiconductor imaging detectors have been developed for use in a Si/CdTe Compton camera. Based on a previous study using the first prototype of a Si/CdTe Compton camera, new detector modules have been designed to upgrade the performance of the Compton camera. As the scatter detector of the Compton camera, a stack of double-sided Si strip detector (DSSD) modules, which has four layers with a stack pitch of 2mm, was constructed. By using the stack DSSDs, an energy resolution of 1.5keV (FWHM) was achieved. For the absorber detector, the CdTe pixel detector modules were built and a CdTe pixel detector stack using these modules was also constructed. A high energy resolution (Delta E/E similar to 1%) was achieved. The improvement of the detection efficiency by stacking the modules has been confirmed by tests of the CdTe stack. Additionally, a large area CdTe imager is introduced as one application of the CdTe pixel detector module. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nima.2007.05.306

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST PURE APPLIED PHYSICS  

We developed a new At Schottky CdTe pixel detector and measured its spectral performance. It has pixelated anodes made of aluminum and a common cathode made of platinum. Because of the low leakage current and the high bias voltage owing to the Schottky diode characteristic and the anode pixel configuration, a good spectral performance including a high energy resolution was achieved. When the pixel detector with a thickness of 0.75 mm was subjected to a bias voltage of 400 V and was operated at -20 degrees C, the full-width-half-maximum (FWHM) energy resolution of 1.1 and 1.8keV at 59.5 and 122keV, respectively, were successfully obtained. The spectral performance obtained with the At Schottky CdTe pixel detector exceeded that obtained with the conventional In Schottky CdTe pixel detector, which has an In common anode and Pt pixelated cathodes, under the same operating conditions.

DOI： 10.1143/JJAP.46.6043

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We developed Schottky CdTe detectors using At 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 At 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 degrees C and a bias voltage of 400 V. Using the same technology, we next developed 8 x 8 pixel Me detectors, again with the four different thicknesses. The At anode electrode was pixelated and the Pt cathode was made as a, single plate. Signals from all pixels were successfully obtained and all 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 degrees 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.

DOI： 10.1117/12.735188

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

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 similar to 2.5 degrees, thanks to the high energy resolution in both the DSSD and CdTe parts.

DOI： 10.1117/12.733840

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