Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Hashimoto, Shoji*; Tanaka, Taku*; Komatsu, Masabumi*; Gonze, M.-A.*; Sakashita, Wataru*; Kurikami, Hiroshi; Nishina, Kazuya*; Ota, Masakazu; Ohashi, Shinta*; Calmon, P.*; et al.
Journal of Environmental Radioactivity, 238-239, p.106721_1 - 106721_10, 2021/11
Times Cited Count：11 Percentile：56.59(Environmental Sciences)This study was aimed at analysing performance of models for radiocesium migration mainly in evergreen coniferous forest in Fukushima, by inter-comparison between models of several research teams. The exercise included two scenarios of countermeasures against the contamination, namely removal of soil surface litter and forest renewal, and a specific konara oak forest scenario in addition to the evergreen forest scenario. All the models reproduced trend of time evolution of radiocesium inventories and concentrations in each of the components in forest such as leaf and organic soil layer. However, the variations between models enlarged in long-term predictions over 50 years after the fallout, meaning continuous field monitoring and model verification/validation is necessary.
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 
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.
Klotz, S.*; Komatsu, Kazuki*; Polian, A.*; Machida, Shinichi*; Sano, Asami; Iti
, J.-P.*; Hattori, Takanori
Physical Review B, 101(6), p.064105_1 - 064105_6, 2020/02
Times Cited Count：4 Percentile：26.53(Materials Science, Multidisciplinary)Manganese oxide (MnO) is a prototype of an antiferromagnetic Mott-insulator. Here we investigate the interplay of magnetic ordering and lattice distortion across the Nel temperature 
under pressure using neutron and X-ray diffraction. We find an increase of with a rate of 
= +4.5(5) K/GPa, an increase of the rhombohedral distortion 
by 
= +0.018/GPa, as well as a volume striction which is insensitive to pressure. These results allow to retrieve the dependence of the coupling constants 
and 
on interatomic distances and compare it to first-principles predictions. Antiferromagnetic diffuse scattering was observed up to 
1.2 , and long-range magnetic order appears at room temperature at 42 GPa.
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.
-AlOOH under mantle conditions using neutron diffractionSano, Asami; Hattori, Takanori; Komatsu, Kazuki*; Kagi, Hiroyuki*; Nagai, Takaya*; Molaison, J. J.*; Dos Santos, A. M.*; Tulk, C. A.*
Scientific Reports (Internet), 8(1), p.15520_1 - 15520_9, 2018/10
Times Cited Count：43 Percentile：92.48(Multidisciplinary Sciences)The pressure response of hydrogen bond in aluminous hydroxide -AlOOH, which is an important candidate for water carrier to the deep Earth in a subducting slab, was investigated using neutron diffraction under high pressure. The symmetrization of hydrogen bond in which hydrogen locates at the center between two oxygen atoms was observed directly for the first time. The present result indicates that the changes of mineral properties such as increase in bulk modulus and sound velocities, which were previously found, were induced by the symmetrization and disorder state that was also found at just below the symmetrization pressure. Even the symmetrization is a small change in the hydrogen location but it is playing an important role in determining the physical properties of minerals.
Ino, Kohei*; Hernsdorf, A. W.*; Konno, Yuta*; Kozuka, Mariko*; Yanagawa, Katsunori*; Kato, Shingo*; Sunamura, Michinari*; Hirota, Akinari*; Togo, Yoko*; Ito, Kazumasa*; et al.
ISME Journal, 12(1), p.31 - 47, 2018/01
Times Cited Count：49 Percentile：91.33(Ecology)In this study, we found the dominance ofanaerobic methane-oxidizing archaea in groundwater enriched in sulfate and methane from a 300-m deep underground borehole in granitic rock.
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.
Klotz, S.*; Komatsu, Kazuki*; Pietrucci, F.*; Kagi, Hiroyuki*; Ludl, A.-A.*; Machida, Shinichi*; Hattori, Takanori; Sano, Asami; Bove, L. E.*
Scientific Reports (Internet), 6, p.32040_1 - 32040_8, 2016/08
Times Cited Count：27 Percentile：60.26(Multidisciplinary Sciences)It has been known since decades that certain aqueous salt solutions of LiCl and LiBr readily form glasses when cooled to below 
160 K. This fact has recently been exploited to produce a 
salty
high pressure ice form: When the glass is compressed at low temperatures to pressures higher than 4 GPa and subsequently warmed, it crystallizes into ice VII with the ionic species trapped inside the ice lattice. Here we report the extreme limit of salt incorporation into ice VII, using high pressure neutron diffraction and molecular dynamics simulations. We show that high-pressure crystallization of aqueous solutions of LiCl
5.6H
O and LiBr5.6HO leads to solids with strongly expanded volume, a destruction of the hydrogen-bond network with an isotropic distribution of water-dipole moments, as well as a crystal to-amorphous transition on decompression. This highly unusual behavior constitutes an interesting pathway from a glass to a crystal where translational periodicity is restored but the rotational degree of freedoms remaining completely random.
-PIGE/PIXE analysisOkuyama, Katsushi*; Komatsu, Hisanori*; Yamamoto, Hiroko*; Pereira, P. N. R.*; Bedran-Russo, A. K.*; Nomachi, Masaharu*; Sato, Takahiro; Sano, Hidehiko*
Nuclear Instruments and Methods in Physics Research B, 269(20), p.2269 - 2273, 2011/10
Times Cited Count：9 Percentile：57.01(Instruments & Instrumentation)Abe, Hiroshi; Uedono, Akira*; Uchida, Hirohisa*; Komatsu, A.*; Okada, Sohei; Ito, Hisayoshi
Materials Science Forum, 363-365, p.156 - 158, 2001/05
no abstracts in English
Arakawa, Masashi*; Komatsu, Kazuki*; Iizuka, Riko*; Kagi, Hiroyuki; Fernandez-Baca, J. A.*; Chakoumakos, B.*; Yamauchi, Hiroki; Fukazawa, Hiroshi
no journal, ,
We prepared ice XI from different kinds of alkali metal hydroxide solutions with different concentrations, and measured neutron powder diffraction at JRR-3 (Japan Atomic Energy Agency, Japan) and HFIR (Oak Ridge National Laboratory, TN, USA). Rietveld analysis was carried out for the obtained diffraction patterns using a two-phase model, which includes ices Ih and XI. The hydrogen-ordered structure in the lithium-doped ice was the same as that in the sodium-doped and potassium-doped ices. We also confirmed the optimum formation condition of ice XI for the temperature history and concentration of solution. Furthermore, our results indicate that the phase transition from ice Ih to XI occurs in the doped ice that had once been ice XI to a notably larger degree than in the doped ice that had never transformed to ice XI. We named this phenomenon memory effect of hydrogen ordering.
-AlOOH at high pressureSano, Asami; Komatsu, Kazuki*; Hattori, Takanori; Nagai, Takaya*; Kagi, Hiroyuki*; Molaison, J.*; Moreira Dos Santos, A.*; Tulk, C.*
no journal, ,
-AlOOH is a high pressure polymorph of diaspore. Previous theoretical studies predict that hydrogen bond become symmetric at high pressure. Neutron diffraction experiment at high pressure found that O-D bond is elongated at high pressure, in support these predictions. Powder X-ray diffraction studies also found that the change in compressibility occurs at high pressure. To investigate the sequence to the symmetrization and its relation with the change in compressibility, we conducted neutron diffraction experiments on -AlOOH was conducted at SNAP, SNS. The results suggest the transition from hydrogen ordered structure to disordered structure at 6.7 GPa. Strong DH isotope effect was also found in the hydrogen bond geometry at high pressure.
Hashimoto, Shoji*; Tanaka, Taku*; Komatsu, Masabumi*; Gonze, M.-A.*; Sakashita, Wataru*; Kurikami, Hiroshi; Nishina, Kazuya*; Ota, Masakazu; Ohashi, Shinta*; Calmon, P.*; et al.
no journal, ,
We applied modelling approaches to evaluate the past and future dynamics of 
Cs in forests. In the model inter-comparison exercise using Fukushima data, six models with diverse model structures, processes, parameters and numerical approaches joined this exercise and the performance and uncertainties of the state-of-the-art models were explored. The inter-comparison revealed that, after appropriate calibration, the models reproduced the observed data reliably and the ranges of calculated trajectories were narrow in the early phase after the fallout. However, the envelope of the calculated model end points enlarged in long-term simulations over 50 years after the fallout. The model-inter comparison exercise emphasizes the importance of decadal data for various forest types and repetitive verification/validation processes using holistic, long-term data to improve the models and to update the forecasting capacity of the models.
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.
Nakashima, Shinsuke*; Komatsu, Ren*; Alessandro, M.*; Fraggasso, A.*; Woo, H.*; Matsuhira, Nobuto*; Kawabata, Kuniaki; Asama, Hajime*
no journal, ,
