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O
) by mechanochemical treatmentAkiyama, Daisuke*; Mishima, Tomoki*; Okamoto, Yoshihiro; Kirishima, Akira*
High Temperature Materials and Processes, 42(1), p.20220268_1 - 20220268_9, 2023/04
A powder mixture of UO and TiO was mechanochemically treated in a planetary ball mill under Ar atmosphere for 1 h using a tungsten carbide vial and balls as the milling medium. Such mechanochemical (MC) treatment reduced the crystallinity of UO and TiO. The mechanochemically treated powder mixture was heated at 973-1573K for 6 h under Ar atmosphere and analyzed by X-ray diffraction analysis, scanning electron microscopy-energy-dispersive X-ray spectroscopy, and X-ray absorption fine structure analysis. UTiO did not form below 1373K without MC treatment and only the starting materials were observed. At 1473 and 1573K, a small amount of UTiO and equal amounts of UTiO and UO were formed, respectively. The mechanochemically treated sample produced nearly pure UTiO containing small amounts of UO impurities when heated above 1173K for 6 h. UTiO was highly crystalline and uniform regardless of the synthesis temperature.
Sueoka, Shigeru; Iwano, Hideki*; Danhara, Toru*; Okamoto, Akira*; Tagami, Takahiro*
Fisshion, Torakku Nyusureta, (35), p.1 - 4, 2022/12
no abstracts in English
Nagata, Mitsuhiro; Fukuda, Shoma; Sueoka, Shigeru; Nakajima, Toru; Kajita, Yuya*; Minami, Saki*; Okamoto, Akira*; Tagami, Takahiro*
Fisshion, Torakku Nyusureta, (35), p.15 - 18, 2022/09
We performed U-Pb dating on zircons from the Utaosa Rhyolite of the Teragi Group as part of the search for standard materials for dating of zircons. Previous studies about Utaosa Rhyolite have reported ca. 2.30-2.77 Ma zircon fission track, zircon (U-Th)/He, and biotite K-Ar ages. U-Pb dating was carried out on the multi-collector inductively coupled plasma mass spectrometer with a laser ablation system. The weighted mean 
U-
Pb ages of 2.65
0.16 Ma and 2.660.15 Ma were obtained from two samples. These ages are consistent with the ages from the previous studies. Therefore the results show that zircons from the Utaosa Rhyolite may be effective as a standard material.
and CrUOAkiyama, Daisuke*; Kusaka, Ryoji; Kumagai, Yuta; Nakada, Masami; Watanabe, Masayuki; Okamoto, Yoshihiro; Nagai, Takayuki; Sato, Nobuaki*; Kirishima, Akira*
Journal of Nuclear Materials, 568, p.153847_1 - 153847_10, 2022/09
Times Cited Count：3 Percentile：66.21(Materials Science, Multidisciplinary)FeUO, CrUO, and Fe
Cr
UO are monouranates containing pentavalent U. Even though these compounds have similar crystal structures, their formation conditions and thermal stability are significantly different. To determine the factors causing the difference in thermal stability between FeUO and CrUO, their crystal structures were evaluated in detail. A Raman band was observed at 700 cm
in all the samples. This Raman band was derived from the stretching vibration of the O-U-O axis band, indicating that FeCrUO was composed of a uranyl-like structure in its lattice regardless of its "x"' value. M
ssbauer measurements indicated that the Fe in FeUO and FeCrUO were trivalent. Furthermore, FeCrUO lost its symmetry around Fe
with increasing electron densities around Fe, as the abundance of Cr increased. These results suggested no significant structural differences between FeUO and CrUO. Thermogravimetric measurements for UO, FeUO, and CrUO showed that the temperature at which FeUO decomposed under an oxidizing condition (approximately 800 
C) was significantly lower than the temperature at which the decomposition of CrUO started (approximately 1250 C). Based on these results, we concluded that the decomposition of FeUO was triggered by an "in-crystal" redox reaction, i.e., Fe 
U
Fe
U
, which would not occur in the CrUO lattice because Cr could never be reduced under the investigated condition. Finally, the existence of Cr in FexCrUO effectively suppressed the decomposition of the FeCrUO crystal, even at a very low Cr content.
Kirishima, Akira*; Terasaki, Mariko*; Miyakawa, Kazuya; Okamoto, Yoshihiro; Akiyama, Daisuke*
Chemosphere, 289, p.133181_1 - 133181_12, 2022/04
Times Cited Count：1 Percentile：5.8(Environmental Sciences)no abstracts in English
Nagai, Takayuki; Akiyama, Daisuke*; Kirishima, Akira*; Sato, Nobuaki*; Okamoto, Yoshihiro
2020-Nendo "Busshitsu, Debaisu Ryoiki Kyodo Kenkyu Kyoten" Oyobi "Hito, Kankyo To Busshitsu O Tsunagu Inobeshion Soshutsu Dainamikku, Araiansu" Kenkyu Seika, Katsudo Hokokusho (CD-ROM), 1 Pages, 2021/11
no abstracts in English
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.
Nagai, Takayuki; Akiyama, Daisuke*; Kirishima, Akira*; Sato, Nobuaki*; Okamoto, Yoshihiro
2019-Nendo "Busshitsu, Debaisu Ryoiki Kyodo Kenkyu Kyoten" Oyobi "Hito, Kankyo To Busshitsu O Tsunagu Inobeshion Soshutsu Dainamikku, Araiansu" Kenkyu Seika, Katsudo Hokokusho (CD-ROM), P. 20191107_1, 2020/11
no abstracts in English
Noda, Akira*; Nakao, Masao*; Okamoto, Hiromi*; Osaki, Kazuya*; Yuri, Yosuke; Soda, Hikaru*; Tongu, Hiromu*; Jimbo, Koichi*; Grieser, M.*; He, Z.*; et al.
Proceedings of 5th International Particle Accelerator Conference (IPAC '14) (Internet), p.28 - 33, 2014/07
Noda, Akira*; Nakao, Masao*; Soda, Hikaru*; Tongu, Hiromu*; Okamoto, Hiromi*; Osaki, Kazuya*; Yuri, Yosuke; Jimbo, Koichi*; Grieser, M.*; He, Z.*
Proceedings of 10th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.143 - 145, 2014/06
Yuri, Yosuke; Osaki, Kazuya*; Okamoto, Hiromi*; He, Z.*; Soda, Hikaru*; Noda, Akira*; Nakao, Masao*; Tongu, Hiromu*; Jimbo, Koichi*
Proceedings of Workshop on Beam Cooling and Related Topics (COOL '13) (Internet), p.162 - 165, 2013/11
Noda, Akira*; Nakao, Masao*; Soda, Hikaru*; Tongu, Hiromu*; Okamoto, Hiromi*; Osaki, Kazuya*; Yuri, Yosuke; Jimbo, Koichi*; Grieser, M.*; He, Z.*
Proceedings of Workshop on Beam Cooling and Related Topics (COOL '13) (Internet), p.157 - 161, 2013/11
He, Z.*; Wei, J.*; Osaki, Kazuya*; Okamoto, Hiromi*; Noda, Akira*; Nakao, Masao*; Soda, Hikaru*; Yuri, Yosuke; Jimbo, Koichi*
Proceedings of 25th North American Particle Accelerator Conference (NA-PAC '13) (Internet), p.1298 - 1300, 2013/09
Soda, Hikaru*; Nakao, Masao*; Tongu, Hiromu*; Jimbo, Koichi*; Osaki, Kazuya*; Okamoto, Hiromi*; Yuri, Yosuke; He, Z.*; Grieser, M.*; Noda, Akira*
Japanese Journal of Applied Physics, 52(3), p.030202_1 - 030202_4, 2013/03
Times Cited Count：5 Percentile：22.74(Physics, Applied)Noda, Akira*; Nakao, Masao*; Soda, Hikaru*; Tongu, Hiromu*; Jimbo, Koichi*; Okamoto, Hiromi*; Osaki, Kazuya*; Yuri, Yosuke; Meshkov, I.*; Smirnov, A.*; et al.
Proceedings of 23rd Russian Particle Accelerator Conference (RuPAC 2012) (Internet), p.48 - 52, 2012/09
Soda, Hikaru*; Nakao, Masao*; Tongu, Hiromu*; Noda, Akira*; Jimbo, Koichi*; Osaki, Kazuya*; Okamoto, Hiromi*; Yuri, Yosuke; Grieser, M.*; He, Z.*
Proceedings of 9th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.388 - 390, 2012/08
no abstracts in English
Noda, Akira*; Nakao, Masao*; Soda, Hikaru*; Tongu, Hiromu*; Jimbo, Koichi*; Okamoto, Hiromi*; Osaki, Kazuya*; Yuri, Yosuke; Grieser, M.*; He, Z.*
Proceedings of 9th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.72 - 74, 2012/08
Soda, Hikaru*; Nakao, Masao*; Noda, Akira*; Tongu, Hiromu*; Ito, Kiyokazu*; Okamoto, Hiromi*; Yuri, Yosuke; Jimbo, Koichi*; Grieser, M.*; He, Z.*
Proceedings of 3rd International Particle Accelerator Conference (IPAC '12) (Internet), p.397 - 399, 2012/05
Noda, Akira*; Nakao, Masao*; Soda, Hikaru*; Tongu, Hiromu*; Ito, Kiyokazu*; Okamoto, Hiromi*; Osaki, Kazuya*; Yuri, Yosuke; Jimbo, Koichi*; Grieser, M.*; et al.
Proceedings of 3rd International Particle Accelerator Conference (IPAC '12) (Internet), p.394 - 396, 2012/05
absorption edgesOkane, Tetsuo; Takeda, Yukiharu; Okamoto, Jun*; Mamiya, Kazutoshi*; Okochi, Takuo; Fujimori, Shinichi; Saito, Yuji; Yamagami, Hiroshi; Fujimori, Atsushi; Ochiai, Akira*; et al.
Journal of the Physical Society of Japan, 77(2), p.024706_1 - 024706_6, 2008/02
Times Cited Count：15 Percentile：64.33(Physics, Multidisciplinary)