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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：49 Percentile：96.63(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：282 Percentile：99.70(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, Takahiro*; Kitazato, Kohei*; Abe, Masanao*; Otake, Makiko*; Arai, Takehiko*; Arai, Tomoko*; Hirata, Naru*; Hiroi, Takahiro*; Honda, Chikatoshi*; Imae, Naoya*; et al.
Space Science Reviews, 208(1-4), p.317 - 337, 2017/07
Times Cited Count：54 Percentile：69.65(Astronomy & Astrophysics)NIRS3: The Near Infrared Spectrometer is installed on the Hayabusa2 spacecraft to observe the target C-type asteroid 162173 Ryugu at near infrared wavelengths of 1.8 to 3.2 micrometer. It aims to obtain reflectance spectra in order to detect absorption bands of hydrated and hydroxide minerals in the 3 micrometer-band. We adopted a linear-image sensor with indium arsenide (InAs) photo diodes and a cooling system with a passive radiator to achieve an optics temperature of 188 K, which enables to retaining sufficient sensitivity and noise level in the 3 micrometer wavelength region. We conducted ground performance tests for the NIRS3 flight model (FM) to confirm its baseline specifications. The results imply that the properties such as the signal-to-noise ratio (SNR) conform to scientific requirements to determine the degree of aqueous alteration, such as CM or CI chondrite, and the stage of thermal metamorphism on the asteroid surface.
Haba, Hiromitsu*; Tsukada, Kazuaki; Asai, Masato; Toyoshima, Atsushi; Akiyama, Kazuhiko; Nishinaka, Ichiro; Hirata, Masaru; Yaita, Tsuyoshi; Ichikawa, Shinichi; Nagame, Yuichiro; et al.
Journal of the American Chemical Society, 126(16), p.5219 - 5224, 2004/04
Times Cited Count：44 Percentile：72.71(Chemistry, Multidisciplinary)Fluoride complexation of element 104, rutherfordium (Rf), produced in the 
Cm(
O,5n)
Rf reaction has been studied by anion-exchange chromatography on an atom-at-a-time scale. The anion-exchangechromatographic behavior of Rf was investigated in 1.9-13.9 M hydrofluoric acid together with those of the group-4 elements Zr and Hf produced in the O-induced reactions on Ge and Gd targets, respectively. It was found that the adsorption behavior of Rf on anion-exchange resin is quite different from those of Zr and Hf, suggesting the influence of relativistic effect on the fluoride complexation of Rf.
Sato, Takumi; Hirata, Naoya*; Oikawa, Katsunari*; Nagae, Yuji; Kurata, Masaki
no journal, ,
Macroscopic segregation of molten core and melt components occurs with slow cooling rate in the accident of Fukushima Daiichi Nuclear Power Plants. In this study, solidification and microscopic segregation are simulated with the Scheil model and thermal properties calculated by Thermo-calc in order to investigate an influence of cooling conditions on macroscopic segregation. A macroscopic segregation behaviour has been calculated for UO
-ZrO-FeO system, which are major oxides of molten core materials. According to calculated results, UO and ZrO was concentrated in initial solidification area. On the other hand, FeO were strongly concentrated in later solidification area. In addition, macroscopic segregation tends to be suppressed in the conditions of fast solidification rate and slow velocity of solidification interface.
Sato, Takumi; Hirata, Naoya*; Oikawa, Katsunari*; Nagae, Yuji; Kurata, Masaki
no journal, ,
Macroscopic segregation of molten core and melt components occurs with slow cooling rate in the accident of Fukushima Daiichi Nuclear Power Plants. In this study, solidification and microscopic segregation are simulated with the Scheil model and thermal properties calculated by Thermo-calc in order to investigate an influence of cooling conditions on macroscopic segregation. A macroscopic segregation behaviour has been calculated for UO-ZrO-FeO system, which are major oxides of molten core materials in various conditions. According to calculated results, UO and ZrO were concentrated in initial solidification area. On the other hand, FeO was strongly concentrated in later solidification area. FeO was significantly segregated because FeO does not be dissolved in UO and ZrO. In addition, macroscopic segregation tends to become stronger in the conditions of slow solidification rate and fast velocity of solidification interface.
Sato, Takumi; Hirata, Naoya*; Oikawa, Katsunari*; Nagae, Yuji; Kurata, Masaki
no journal, ,
Macroscopic segregation of molten core and melted components occurs with slow cooling rate in the accident of Fukushima Daiichi Nuclear Power Plants. The solidification model considering macroscopic segregation of molten core and melted components was developed in order to predict distribution of core elements. In this study, solidification and microscopic segregation were simulated with the Scheil model using thermal properties calculated by Thermo-calc. We estimated segregation behavior of molten core and investigated an influence of cooling conditions on macroscopic segregation.
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.
Ogawa, Tatsuhiko; Iwamoto, Yosuke; Hashimoto, Shintaro; Sato, Tatsuhiko; Matsuda, Norihiro; Kunieda, Satoshi; 
elik, Y.*; Furutachi, Naoya*; Niita, Koji*; Furuta, Takuya; et al.
no journal, ,
PHITS is a general-purpose radiation transport simulation code that has been developed mainly by JAEA in cooperation with domestic and foreign research institutes. We released the latest version, PHITS 3.27, in March 2022. Since SATIF-14 held in 3 years ago, following updates were implemented (1)Extension of the cross section data reading module, (2)Modernization of burn-up calculation code DCHAIN, (3)Functionality to calculate the dependence of the result on the input parameters, (4)Interactive 3D geometry viewer,PHIG-3D, (5)Cosmic ray source function, (6)Track-structure calculation models, which calculate the atomic-scale reactions of charged particles on event-by-event basis, for electrons, positions, and heavy ions, (7)GUI-version RT-PHITS development, (8)random number generation by Xor-shift64 algorithm, (9)User-defined stopping power reading module, (10)EXFOR data reading module, (11)Photon-induced mu-mu pair production model. In addition, a bench, ark study conducted by Iwamoto et al, is also presented to explain the importance of the new cross section reading module.
