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Journal Articles

Thermally altered subsurface material of asteroid (162173) Ryugu

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:43 Percentile:96.93(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 $$^{circ}$$C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 $$^{circ}$$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.

Journal Articles

The Surface composition of asteroid 162173 Ryugu from Hayabusa2 near-infrared spectroscopy

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:259 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.

Journal Articles

Microanalysis of silica-based adsorbent for effective recovery of radioactive elements

Sano, Yuichi; Watanabe, So; Matsuura, Haruaki*; Nagoshi, Kohei*; Arai, Tsuyoshi*

Journal of Nuclear Science and Technology, 54(10), p.1058 - 1064, 2017/10

 Times Cited Count:5 Percentile:37.06(Nuclear Science & Technology)

For effective recovery of radioactive elements by adsorbents using polymer-immobilized silica (SiO$$_{2}$$-P) supports, the microstructure of SiO$$_{2}$$-P particles impregnated with CMPO as extractants and their change with the crosslinking degree of polymer (CDP) were investigated using STXM and EXAFS analyses; further, their relation with adsorption/elution behavior was discussed. The adsorption/elution tests using adsorbents with a different CDP demonstrated that a higher CDP inhibited the elution of adsorbed metal ions from the adsorbent. The results of STXM and EXAFS analyses suggested that adsorption by CMPO proceeds through the entire area in the adsorbent and the local structure around adsorbed metal ions is similar irrespective of the CDP. Conversely, STXM analyses implied the capture of eluents such as H$$_{2}$$O by polymers with high CDP, which suppresses the prompt elution of adsorbed metal ions from the adsorbent.

Journal Articles

Maximizing $$T_c$$ by tuning nematicity and magnetism in FeSe$$_{1-x}$$S$$_x$$ superconductors

Matsuura, Kohei*; Mizukami, Yuta*; Arai, Yuki*; Sugimura, Yuichi*; Maejima, Naoyuki*; Machida, Akihiko*; Watanuki, Tetsu*; Fukuda, Tatsuo; Yajima, Takeshi*; Hiroi, Zenji*; et al.

Nature Communications (Internet), 8, p.1143_1 - 1143_6, 2017/10

 Times Cited Count:80 Percentile:91.57(Multidisciplinary Sciences)

Journal Articles

Microscopic analyses of complexes formed in adsorbent for Mo and Zr separation chromatography

Abe, Ryoji*; Nagoshi, Kohei*; Arai, Tsuyoshi*; Watanabe, So; Sano, Yuichi; Matsuura, Haruaki*; Takagi, Hideaki*; Shimizu, Nobutaka*; Koka, Masashi*; Sato, Takahiro*

Nuclear Instruments and Methods in Physics Research B, 404, p.173 - 178, 2017/08

 Times Cited Count:5 Percentile:44.54(Instruments & Instrumentation)

Journal Articles

NIRS3; The Near Infrared Spectrometer on Hayabusa2

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:71.62(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.

Journal Articles

Multi-quasiparticle states and ${it K}$-forbidden transitions in $$^{183}$$Os

Shizuma, Toshiyuki; Matsuura, Katsuyuki*; Toh, Yosuke; Hayakawa, Takehito; Oshima, Masumi; Hatsukawa, Yuichi; Matsuda, Makoto; Furuno, Kohei*; Sasaki, Yasuyuki*; Komatsubara, Tetsuro*; et al.

Nuclear Physics A, 696(3-4), p.337 - 370, 2001/12

 Times Cited Count:20 Percentile:73.84(Physics, Nuclear)

High-spin states in $$^{183}$$Os have been studied using the 170Er(18O,5n) reaction at a beam energy of 85 MeV. Nine rotational bands based on 1-, 3-, 5- and 7-quasiparticle excitations have been observed. Nilsson configurations are assigned for the newly observed bands using g-factors deduced from M1/E2 branching ratios within the bands. In addition, two isomers with K=(43/2+) and (43/2-) have been identified. The K=(43/2+) isomer decays directly to the K=9/2+ ground state band with a large difference in the $$K$$ quantum number, $$mitDelta K=$$17. The decay rates are disccused in terms of a tunneling model where high-$$K$$ (isomeric) and low-$$K$$ states interact via fluctuations towards triaxial nuclear shapes.

Oral presentation

Spectral characteristics of asteroid (162173) Ryugu with Hayabusa2 NIRS3

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.

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