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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：97.1(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.
Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; Matsuoka, Moe*; et al.
Science, 364(6437), p.272 - 275, 2019/04
Times Cited Count：262 Percentile：99.73(Multidisciplinary Sciences)The near-Earth asteroid 162173 Ryugu, the target of Hayabusa2 sample return mission, is believed to be a primitive carbonaceous object. The Near Infrared Spectrometer (NIRS3) on Hayabusa2 acquired reflectance spectra of Ryugu's surface to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micron was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally- and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.
Tampo, Motonobu; Awano, Shinya*; Bolton, P.; Kondo, Kiminori; Mima, Kunioki*; Mori, Yoshitaka*; Nakamura, Hirotaka*; Nakatsutsumi, Motoaki*; Stephens, R. B.*; Tanaka, Kazuo*; et al.
Physics of Plasmas, 17(7), p.073110_1 - 073110_5, 2010/07
Times Cited Count：12 Percentile：42.34(Physics, Fluids & Plasmas)Nakamura, Hirotaka*; Chrisman, B.*; Tanimoto, Tsuyoshi*; Borghesi, M.*; Kondo, Kiminori; Nakatsutsumi, Motoaki*; Norimatsu, Takayoshi*; Tampo, Motonobu; Tanaka, Kazuo*; Yabuuchi, Toshinori*; et al.
Physical Review Letters, 102(4), p.045009_1 - 045009_4, 2009/01
Times Cited Count：23 Percentile：73.34(Physics, Multidisciplinary)Interactions between a relativistic-intensity laser pulse and a cone-wire target are studied by changing the focusing point of the pulse. The pulse, when focused on the sidewall of the cone, produced superthermal electrons with an energy 
10 MeV, whereas less energetic electrons 
1 MeV were produced by the pulse when focused on the cone tip. Efficient heating of the wire was indicated by significant neutron signals observed when the pulse was focused on the tip. Particle-in-cell simulation results show reduced heating of the wire due to energetic electrons produced by specularly reflected light at the sidewall.
Nakamura, Hirotaka*; Sentoku, Yasuhiko*; Matsuoka, Takeshi*; Kondo, Kiminori; Nakatsutsumi, Motoaki*; Norimatsu, Takayoshi*; Shiraga, Hiroyuki*; Tanaka, Kazuo*; Kodama, Ryosuke*
Physical Review Letters, 100(16), p.165001_1 - 165001_4, 2008/04
Times Cited Count：15 Percentile：64.33(Physics, Multidisciplinary)We produced cylindrically imploded plasmas, which have the same density-radius product of the imploded plasma 
R with the compressed core in the fast ignition experiment and demonstrated efficient fast heating of cylindrically imploded plasmas with an ultraintense laser light. The coupling efficiency from the laser to the imploded column was 14%-21%, implying strong collimation of energetic electrons over a distance of 300 micron of the plasma. Particle-in-cell simulation shows confinement of the energetic electrons by self-generated magnetic and electrostatic fields excited along the imploded plasmas, and the efficient fast heating in the compressed region.
Yamanaka, Atsushi; Sato, Takehiko; Nakajima, Masayoshi; Ishiyama, Koichi; Uchida, Naoki; Sumi, Hirotaka; Omura, Masami
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Murakami, Manabu; Sato, Takehiko; Nakajima, Masayoshi; Ishiyama, Koichi; Uchida, Naoki; Sumi, Hirotaka; Omura, Masami
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Sumi, Hirotaka; Ito, Yoshiyuki; Fujiwara, Koji; Ueno, Tsutomu
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He polarized neutron spin filters and its present status, 2Kira, Hiroshi; Sakaguchi, Yoshifumi; Oku, Takayuki; Suzuki, Junichi; Nakamura, Mitsutaka; Arai, Masatoshi; Endo, Yasuo; Kakurai, Kazuhisa; Arimoto, Yasushi*; Ino, Takashi*; et al.
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Kawasumi, Hiroyuki; Sanyoshi, Hirotaka; Yatogi, Hideo; Fukuari, Yoshihiro; Inami, Shinichi
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In the ventilation facilities of the Tokai reprocessing plant, particle filters are generally installed both in air-intake and exhaust systems. In the air-intake system, atmospheric dust is filtered and the cleaned air is supplied into radiation controlled areas, whereas in the exhaust system, radioactive materials are filtered and discharge it to the environment. Because the filter of the exhaust system serves to prevent radiological release to the environment, a high-efficiency particle air (HEPA) filter that a decontamination factor is extremely high, is used for filtering radioactive particles. The HEPA filter is usually exchanged with new one when the filter is carried over with particles, or it is exchanged by the limit as an anti-aging deterioration measure in time. This report reviews the exchange period of a periodical filter by confirming the integrity of a filter installed in investigation and the enforcement of the past filter exchange results and reports the result that planned adequacy.
Matsumura, Tadayuki; Takaya, Akikazu; Sumi, Hirotaka; Ishii, Kiyonori; Niitsuma, Koichi; Kodaka, Akira; Fujiwara, Koji
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Kuboki, Michikatsu; Naito, Masakazu; Sumi, Hirotaka; Nakayama, Jiro; Kano, Shigeru; Niitsuma, Koichi; Kodaka, Akira; Fujiwara, Koji
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Nakayama, Jiro; Sumi, Hirotaka; Kuboki, Michikatsu; Kodaka, Akira; Fujiwara, Koji
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Sumi, Hirotaka; Nakayama, Jiro; Kuboki, Michikatsu; Kodaka, Akira; Fujiwara, Koji
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Kawasumi, Hiroyuki; Takeuchi, Kenji; Domura, Kazuyuki; Sanyoshi, Hirotaka; Inami, Shinichi
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The Tokai Reprocessing Plant has recovered nuclear materials from spent nuclear fuel. Reprocessing process is consisted of shearing process, a dissolution process and an extraction process etc. Each facilities designed to confine radioactive materials in controlled area to keep negative pressure using ventilation system. This system has been used over 40 years. We analyzed influences to the trouble of aging equipment, and we considered necessary additional check out system to prevent troubles based on the results of analysis. This reports describe the present status of this system.
Sumi, Hirotaka; Makigaki, Hikaru; Nakayama, Jiro; Niitsuma, Koichi; Kodaka, Akira
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Matsumura, Tadayuki; Sumi, Hirotaka; Tokoro, Takeshi; Yamauchi, Sho; Sato, Shohei; Kano, Shigeru; Morikawa, Yo
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Hasemi, Hiroyuki; Tatsumi, Kazuyoshi; Sato, Hirotaka*; Kamiyama, Takashi*
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Takir, D.*; Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; et al.
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JAXA spacecraft and sample return mission Hayabusa2 has arrived at the near-Earth asteroid 162173 Ryugu, which is classified a primitive carbonaceous object. Here we report recent results of near-infrared spectrometer (NIRS3) on the Hayabusa2 spacecraft. The observations provide direct measurements of the surface composition of Ryugu and context for the returned samples. NIRS3 has detected a weak and narrow absorption feature centered at 2.72 micrometer across entire observed surface. This absorption feature is attributed to the presence of OH-bearing minerals. The NIRS3 observations also revealed that Ryugu is the darkest object to be observed up-close by a visiting spacecraft. The intensity of the OH feature and low albedo are consistent with thermally-and/or shock-metamorphosed, and/or carbon-rich space-weathered primitive and hydrated carbonaceous chondrites.
Lan, Z.*; Yogo, Akifumi*; Hayakawa, Takehito*; Wei, T.*; Kamiyama, Takashi*; Sato, Hirotaka*; Arikawa, Yasunobu*; Mirfayzi, R.*; Koizumi, Mitsuo; Abe, Yuki*; et al.
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