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Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.
Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03
Times Cited Count：44 Percentile：96.99(Astronomy & Astrophysics)Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 
C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.
Yamaguchi, Mitsutaka; Torikai, Kota*; Kawachi, Naoki; Shimada, Hirofumi*; Sato, Takahiro; Nagao, Yuto; Fujimaki, Shu; Kokubun, Motohide*; Watanabe, Shin*; Takahashi, Tadayuki*; et al.
Physics in Medicine & Biology, 61(9), p.3638 - 3644, 2016/05
Times Cited Count：9 Percentile：100.00(Engineering, Biomedical)no abstracts in English
Yamaguchi, Mitsutaka; Nagao, Yuto; Kawachi, Naoki; Sato, Takahiro; Fujimaki, Shu; Kamiya, Tomihiro; Torikai, Kota*; Shimada, Hirofumi*; Sugai, Hiroyuki*; Sakai, Makoto*; et al.
International Journal of PIXE, 26(1&2), p.61 - 72, 2016/00
no abstracts in English
Yamaguchi, Mitsutaka; Torikai, Kota*; Kawachi, Naoki; Shimada, Hirofumi*; Sato, Takahiro; Nagao, Yuto; Fujimaki, Shu; Kokubun, Motohide*; Watanabe, Shin*; Takahashi, Tadayuki*; et al.
Proceedings of 2013 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC), 2 Pages, 2013/00
Yamaguchi, Mitsutaka; Nagao, Yuto; Kawachi, Naoki; Fujimaki, Shu; Kamiya, Tomihiro; Odaka, Hirokazu*; Kokubun, Motohide*; Takeda, Shinichiro*; Watanabe, Shin*; Takahashi, Tadayuki*; et al.
Proceedings of 2013 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC), 3 Pages, 2013/00
Yamaguchi, Mitsutaka; Torikai, Kota*; Kawachi, Naoki; Shimada, Hirofumi*; Sato, Takahiro; Nagao, Yuto; Fujimaki, Shu; Kokubun, Motohide*; Watanabe, Shin*; Takahashi, Tadayuki*; et al.
Physics in Medicine & Biology, 57(10), p.2843 - 2856, 2012/05
Times Cited Count：41 Percentile：79.69(Engineering, Biomedical)Yamaguchi, Mitsutaka; Nagao, Yuto; Kawachi, Naoki; Fujimaki, Shu; Arakawa, Kazuo*; Kamiya, Tomihiro; Odaka, Hirokazu*; Kokubun, Motohide*; Takeda, Shinichiro*; Watanabe, Shin*; et al.
no journal, ,
no abstracts in English
Yamaguchi, Mitsutaka; Nagao, Yuto; Sugai, Hiroyuki*; Sakai, Makoto*; Kawachi, Naoki; Sato, Takahiro; Kamiya, Tomihiro; Fujimaki, Shu; Arakawa, Kazuo*; Narumi, Kazumasa
no journal, ,
no abstracts in English
Yamaguchi, Mitsutaka; Sakai, Makoto*; Nagao, Yuto; Kawachi, Naoki; Fujimaki, Shu; Arakawa, Kazuo*; Kamiya, Tomihiro; Odaka, Hirokazu*; Kokubun, Motohide*; Takeda, Shinichiro*; et al.
no journal, ,
no abstracts in English
rays by body tissue on the image of semiconductor Compton camera for nuclear medical useSakai, Makoto*; Kikuchi, Kimiko*; Torikai, Kota*; Arakawa, Kazuo*; Yamaguchi, Mitsutaka; Nagao, Yuto; Kawachi, Naoki; Fujimaki, Shu; Kamiya, Tomihiro; Odaka, Hirokazu*; et al.
no journal, ,
no abstracts in English
ray in a body on reconstructed images of Si/CdTe semiconductor Compton camera for medical imagingSakai, Makoto*; Kikuchi, Kimiko*; Torikai, Kota*; Arakawa, Kazuo*; Yamaguchi, Mitsutaka; Nagao, Yuto; Kawachi, Naoki; Fujimaki, Shu; Kamiya, Tomihiro; Odaka, Hirokazu*; et al.
no journal, ,
no abstracts in English
Arakawa, Yuto; Fujii, Katsutoshi; Mimura, Ryuji; Nakashio, Nobuyuki; Onuma, Isamu; Shishido, Nobuhito; Umehara, Takashi
no journal, ,
no abstracts in English
Yamaguchi, Mitsutaka; Nagao, Yuto; Kawachi, Naoki; Fujimaki, Shu; Kamiya, Tomihiro; Torikai, Kota*; Shimada, Hirofumi*; Sugai, Hiroyuki*; Sakai, Makoto*; Arakawa, Kazuo*; et al.
no journal, ,
no abstracts in English
Sakashita, Koichi; Kasugai, Yoshimi; Harada, Masahide; Seki, Kazunari; Sato, Koichi; Kato, Saori; Arakawa, Yuto
no journal, ,
no abstracts in English
Masuyama, Koichi; Arakawa, Yuto; Otsuka, Yoshikazu; Yokosuka, Yoshiyuki; Kobayashi, Makoto; Akiyama, Isamu; Shimizu, Isamu
no journal, ,
no abstracts in English
Sakashita, Koichi; Arakawa, Yuto; Kasugai, Yoshimi; Ishii, Tetsuro
no journal, ,
Radioactive concentration of short-lived gas nuclides produced via air activation by neutron in the hot-cell was measured using a plastic scintillator gas monitor in Materials and Life Science Experimental Facility at J-PARC. However, conversion factors (CF), the ratio of radioactive concentration to count rate, had been unknown for the short-lived nuclides of 
C, 
N and 
O. Therefore we evaluated them with Monte Carlo method using Geant4. As a result, the CF's were shown to be almost constant in the energy region of 
-rays emitted from these short-lived nuclides and 
Ar. Then we adopted the CF of Ar, which is certified by the vendor, as those of the short-lived nuclides.
Kawachi, Naoki; Yamaguchi, Mitsutaka; Nagao, Yuto; Suzui, Nobuo; Fujimaki, Shu; Kamiya, Tomihiro; Odaka, Hirokazu*; Kokubun, Motohide*; Takeda, Shinichiro*; Ishikawa, Shinnosuke*; et al.
no journal, ,
-ray sources at close range using Si/CdTe Compton cameraNagao, Yuto; Yamaguchi, Mitsutaka; Kawachi, Naoki; Fujimaki, Shu; Kamiya, Tomihiro; Takeda, Shinichiro*; Odaka, Hirokazu*; Watanabe, Shin*; Kokubun, Motohide*; Takahashi, Tadayuki*; et al.
no journal, ,
A conventional -ray imaging system such as a gamma camera and SPECT has a fundamental problem that imposes a tradeoff between sensitivity and spatial resolution and restricts -ray energy to low because of the physical constraints resulting from the mechanical collimation. On the other hand, a Compton camera, which applies kinematics of Compton scattering to the electronic collimation, is a next generation -ray imaging system which decouples the tradeoff between sensitivity and spatial resolution and covers a wide range of energy. We study an application of a Si/CdTe semiconductor Compton camera being developed for space observation to in vivo tracer imaging in medicine and biology. Particularly, it is essential for a medical and biological application to estimate quantitative distribution of tracers in a field close to the camera. We developed an image reconstruction method to realize quantitative profiling of -ray emitting sources.
Nagao, Yuto; Yamaguchi, Mitsutaka; Kawachi, Naoki; Fujimaki, Shu; Kamiya, Tomihiro; Takeda, Shinichiro*; Watanabe, Shin*; Takahashi, Tadayuki*; Torikai, Kota*; Arakawa, Kazuo*; et al.
no journal, ,
Nakajima, Junya; Yokosuka, Yoshiyuki; Arakawa, Yuto; Shimizu, Isamu; Umehara, Takashi
no journal, ,
In NUCEF we monitor the radiation level continuously with 81 radiation monitors. Although these monitors are checked periodically, failures have occurred due to various reasons. Then we accumulated all monitor failures which had happened in recent 18 years, and categorized them by reason. This allowed us to find that the number of the failure much differs from monitor to monitor, and that there was a deviation between the reasons of the failure. After that, about degradation of GM tube used as dust monitor, which is by far the most of all reasons, we investigated the relation between the average cps and the interval of exchange. As a result, we couldn't find any causal relationship between the both. On the other hand, to improve the failure situation, we have exchanged expendables periodically, and furthermore, the result of the failure analysis should be fed back for better preventive maintenance.
