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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：66 Percentile：94.57(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：342 Percentile：99.61(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.
Iwata, Mitsunao*; Sugiyama, Yuichi*; Murata, Yoshinori*; Takaya, Shigeru
Defect and Diffusion Forum, 326-328, p.578 - 582, 2012/04
Times Cited Count：0 Percentile：0.00(Nanoscience & Nanotechnology)no abstracts in English
induced by intermetallic charge transferAzuma, Masaki*; Chen, W.*; Seki, Hayato*; Czapski, M.*; Olga, S.*; Oka, Kengo*; Mizumaki, Masaichiro*; Watanuki, Tetsu; Ishimatsu, Naoki*; Kawamura, Naomi*; et al.
Nature Communications (Internet), 2, p.347_1 - 347_5, 2011/06
Times Cited Count：454 Percentile：99.26(Multidisciplinary Sciences)no abstracts in English
Sasa, Toshinobu; Umeno, Makoto*; Mizubayashi, Hiroshi*; Mori, Keijiro*; Futakawa, Masatoshi; Saito, Shigeru; Kai, Tetsuya; Nakai, Kimikazu*; Zako, Akira*; Kasahara, Yoshiyuki*; et al.
JAERI-Tech 2005-021, 114 Pages, 2005/03
JAERI-Tech-2005-021.pdf:9.66MB
To perform the research and development for accelerator-driven system (ADS), Japan Atomic Energy Research Institute (JAERI) plans to build a Transmutation Experimental Facility under the JAERI-KEK joint J-PARC program. Transmutation Experimental Facility consists of two buildings, Transmutation Physics Experimental Facility to make reactor physics experiment with subcritical core, and ADS Target Test Facility for the preparation of irradiation database for various structural materials. In this report, purpose to build, experimental schedule, and design study of the ADS target test facility with drawer type spallation target are summarized.
; A Model for astrobiological studiesHorikawa, Daiki*; Kunieda, Takekazu*; Abe, Wataru*; Koshikawa, Shigeyuki*; Nakahara, Yuichi*; Watanabe, Masahiko*; Iwata, Kenichi*; Sakashita, Tetsuya; Hamada, Nobuyuki*; Higashi, Seigo*; et al.
no journal, ,
We report the first successful rearing of the herbivorous tardigrade, , by supplying a green alga 
as a food. The reared individuals of this species had an anhydrobiotic capacity throughout their life cycle, from eggs, to juveniles, and to adults. Reared adults, while in an anhydrobiotic state, were tolerant to temperatures -196C and 100C. Furthermore, they were shown to be tolerant to the exposure to 99.8% acetonitrile, 1 GPa of hydrostatic pressure, or 5000 Gy of He ion radiation. We will report the details of these results, along with the description of their life history. Due to the observed tolerance to such extreme environmental conditions, we propose R. varieornatus to be included as a suitable model for astrobiological studies of multicellular organisms.
Kishimoto, Yasuaki; Sugiyama, Yuichi*; Iwata, Natsuyo*; Uchida, Tomoyuki*; Fukuda, Yuji
no journal, ,
We have analyzed the dynamics of C atom and CO
clusters irradiated by intense laser pulses by using the EPIC3D code which includes atomic and collisional relaxation processes of plasmas. The parameters were set equal to the experiments conducted by Y. Fukuda et al. at JAEA-KPSI. The interaction processes depend on the average diameter of clusters, the packing fraction, and the random positions of clusters, and the ions, whose energies were comparable to the experiments, was observed. With the dissolution of clusters, the higher level fluctuation structures were created and interesting characters of laser propagation, absorption, and electromagnetic emission were observed.
Kishimoto, Yasuaki; Sugiyama, Yuichi*; Iwata, Natsuyo*; Uchida, Tomoyuki*; Fukuda, Yuji
no journal, ,
Recently, signatures of high energy ion acceleration with 10-20 MeV per nucleon were observed in a clustered medium. A channeling over Rayleigh length was also detected. Here, we studied the characteristics of clustered medium irradiated by high power lasers using a particle based integrated code, EPIC3D, where key physical processes such as ionization, collisional relaxation, radiation damping, etc. are taken into account. The interaction is dominated not only by the averaged quantities, e.g. averaged cluster size and packing fraction, but also by their probabilistic configuration. The generation of high energy ions which range is the same order as the experiments was observed. We also study the propagation dynamics of laser regulated by the cluster expansion and associated complex density profile with high fluctuation level.
Takir, D.*; Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; et al.
no journal, ,
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.
Wadachi, Hiroki*; Kunieda, Takekazu*; Sakashita, Tetsuya; Kawai, Kiyoshi*; Iwata, Kenichi*; Nakahara, Yuichi*; Hamada, Nobuyuki*; Koseki, Shigenobu*; Yamamoto, Kazutaka*; Kobayashi, Yasuhiko; et al.
no journal, ,
We studied the effects of the exposure of extreme environments on life-time and breeding ability of tardigrade 
to reveal the possibility of multi-cellular organism existences in the outerspace. A life time of animals is the shortest in the heavy-ion exposed animals than any other stressors. There were significant decrease in the number of egg-laying and hatching rate between irradiated and non-irradiated animals. However, we found the next generation in all experimental conditions. Our findings suggest that tardigrades exposed to even any extreme environments could have a descendant.
Kishimoto, Yasuaki; Sugiyama, Yuichi*; Iwata, Natsuyo*; Uchida, Tomoyuki*; Fukuda, Yuji
no journal, ,
In order to investigate the laser-driven ion acceleration experiments using cluster-gas targets (CO
clusters + background He gas) conducted by Y. Fukuda et al., we have done a series of simulations using the EPIC3D code, which includes the effects of atomic and collisional relaxation processes. We have analyzed the laser propagation, the absorption of laser light, and the particle acceleration processes inside the targets. As a result, we have found that collimated high energy ions are generated from the rear surface of the targets through a multistep-synergistic manner, such as (1) acceleration of carbon ions due to Coulomb explosion, (2) compression and acceleration of the background helium ions due to electric fields of Coulomb explosion, and ion accelerations due to (3) a magnetic vortex and (4) a sheath field, both of which are formed near the rear surface of the target.
Sugiyama, Yuichi*; Iwata, Mitsunao*; Murata, Yoshinori*; Takaya, Shigeru
no journal, ,
no abstracts in English
Sugiyama, Yuichi*; Iwata, Mitsunao*; Murata, Yoshinori*; Takaya, Shigeru
no journal, ,
no abstracts in English
Iwata, Mitsunao*; Sugiyama, Yuichi*; Murata, Yoshinori*; Takaya, Shigeru
no journal, ,
Microstructural states of metallic materials can be expressed by system free energy, and the estimation of the system free energy is useful for damage analysis of the materials. In this study, change with creep time in the system free energy of the FG-HAZ in 9Cr heat resistant ferritic steels is estimated on the basis of a series of experiments such as chemical analysis by using extracted residues, X-ray diffraction, and scanning transmission observations. The change in the system free energy is expressed quantitatively by rate constants depending on applied stress. It is observed that the steel ruptures when the applied stress exceeds the allowable stress. The relationship between allowable stress and system free energy makes it possible to predict the rupture time in the long term.
Takano, Masahide; Sudo, Ayako; Nakamura, Kinya*; Koyama, Tadafumi*; Uozumi, Koichi*; Kanai, Taizo*; Kanagawa, Shun*; Iwata, Yuichi*; Totsuka, Fumio*; Mogi, Kazutaka*; et al.
no journal, ,
Simulated fuel debris in RPV and CV containing uranium were fabricated by light-concentrating heating technique, respectively, to provide them for cutting tests with disc cutter. Characteristic data such as bulk density, microstructure, formed phases and micro-hardness on cross-section were obtained.
