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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:30 Percentile:97.01(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

$$L_{3}$$-edge jump and shift on white-line of Pd interlayer for trilaminar neutron production target under H$$_{2}$$$$^{+}$$ irradiation

Ishiyama, Shintaro; Fujii, Ryo*; Nakamura, Masaru*; Imahori, Yoshio*

Journal of Chemistry and Chemical Engineering, 8(9), p.870 - 875, 2014/09

Interlayer Pd for the Li/Pd/Cu neutron target for BNCT (Boron Neutron Capture Therapy) was characterized after 0.1-5 keV H$$_{2}$$$$^{+}$$ irradiation by XAFS technique, and following conclusions were derived; (1) From the XAFS observation of white line of Pd, remarkable Pd $$L_{3}$$ Edge jump was found in 1.1-3 times higher than before irradiation in low irradiation fluence. (2) This fact indicates increase of hole density in Pd 4d-band, whereas no change was observed for XASF spectra of Ag sample under the same irradiation conditions. (3) Remarkable Pd $$L_{3}$$ Edge shift of 0.12-0.66 eV was also found with increase of H$$_{2}$$$$^{+}$$ irradiation energy in low fluence, and drastically decreased after peak in high irradiation energy and fluence.(4)Implanted protons deposited in Pd as negative under the balance of electron population enhanced by proton irradiation and charge transfer.

Journal Articles

Low temperature and pressure synthesis of lithium-nitride compound with H$$_{2}$$O addition on lithium target for BNCT

Ishiyama, Shintaro; Baba, Yuji; Fujii, Ryo*; Nakamura, Masaru*; Imahori, Yoshio*

Nihon Kinzoku Gakkai-Shi, 78(8), p.317 - 321, 2014/08

 Times Cited Count:0 Percentile:0.01(Metallurgy & Metallurgical Engineering)

Low temperature synthesis of lithium-nitride compound was conducted on the lithium target for BNCT by N$$_{2}$$/H$$_{2}$$O mixing gas squirt in the ultra high vacuum chamber, and the following results were derived; (1) Lithium-nitride compound was synthesized on the lithium target under 101.3 Pa N$$_{2}$$ gas squirt at room temperature and in the ultra high vacuum chamber under the pressure of 1$$times$$10$$^{-8}$$ Pa. (2) Remarkable contamination by O and C was observed on the lithium-nitride compound synthesized under the squirt pressure of 13.3-80 Pa/1.33-4.7 Pa N$$_{2}$$/H$$_{2}$$O mixing gas. (3) No contamination and synthesis of Li-N compound was observed under the squirt pressure of 0.013-0.027 Pa/0-0.005 Pa N$$_{2}$$/H$$_{2}$$O mixing gas. (4) Contamination by O and C was enhanced with excessive addition of H$$_{2}$$O at the pressure of over 1.33 Pa.

Journal Articles

Surficial chemical states of Li$$_{3}$$N synthesized on lithium target for boron neutron capture therapy

Ishiyama, Shintaro; Baba, Yuji; Fujii, Ryo*; Nakamura, Masaru*; Imahori, Yoshio*

Nihon Kinzoku Gakkai-Shi, 78(8), p.322 - 325, 2014/08

 Times Cited Count:0 Percentile:0.01(Metallurgy & Metallurgical Engineering)

To remove high level of contaminants by O and C from Li$$_{3}$$N surface for boron neutron capture therapy target, high temperature thermal desorption was conducted up to 1123 K in ultra high vacuum and the following results were derived; (1) During thermal desorption up to 1023 K, typical three peaks of vacuum pressure disturbance due to vaporization of contaminants were observed in vacuum pressure-temperature curve. (2) Over-layered contaminants with high melting temperature below 1023 K on Li$$_{3}$$N surface is completely removed by high temperature thermal desorption up to 1123 K in ultra high vacuum. (3) From these desorption results, it is suggested that these contaminants corresponding to these vaporization peaks are H$$_{2}$$O and Li compounds with high melting temperature below 1023 K, of which LiOH and Li$$_{2}$$CO$$_{3}$$ were synthesized by decomposition process of Li$$_{3}$$N with residual H$$_{2}$$O and CO$$_{2}$$ in low temperature.

Journal Articles

Direct synthesis of Li$$_{3}$$N thin layer on lithium target surface for BNCT in N$$_{2}$$ gaseous conditions

Ishiyama, Shintaro; Baba, Yuji; Fujii, Ryo*; Nakamura, Masaru*; Imahori, Yoshio*

Nihon Kinzoku Gakkai-Shi, 78(4), p.137 - 141, 2014/04

 Times Cited Count:0 Percentile:0.01(Metallurgy & Metallurgical Engineering)

To prevent vaporization damage of BNCT (Boron Neutron Capture Therapy) lithium target during operation, direct synthesis of Li$$_{3}$$N thin layer on lithium target surface was demonstrated in 0.1 MPa N$$_{2}$$ gas at temperature below 548 K and the following conclusions were derived; (1) Synthesis of Li$$_{3}$$N thin layer on lithium surface was confirmed after nitridation at 276$$sim$$548 K with surface contamination by oxygen and carbon. (2) Rapid nitridation over 1-5wt.%/min was observed above Li melting temperature, whereas slow reaction under 0.02-0.5 wt.%/min below melting temperature. (3) During nitridation, removal of oxygen contamination on Li$$_{3}$$N thin layer is taken place by nitrogen below Li melting temperature.

Journal Articles

3KeV H$$_{2}$$$$^{+}$$ irradiation to Li/Pd/Cu trilaminar neutron production target for BNCT

Ishiyama, Shintaro; Fujii, Ryo*; Nakamura, Masaru*; Imahori, Yoshio*

Materials Transactions, 55(4), p.658 - 663, 2014/03

 Times Cited Count:2 Percentile:12.41(Materials Science, Multidisciplinary)

The Li/Pd/Cu trilaminar structures of the synthesized target for BNCT were characterized under 3keV H$$_{2}$$$$^{+}$$ irradiation by XPS and XAFS technique, which provides structural/electronic properties of solids, and information about the local structure, such as the nature and number of surrounding atoms and inter-atomic distances. Following conclusions were derived; (1) Pd-Cu physical bonding was produced between the Pd and Cu interface by electro-less plating Pd deposition on a high purity Cu plate (2) From the XAFS observation of white line of Pd, the Pd $$L$$3 Edge jump was found after H$$_{2}$$$$^{+}$$ irradiation, this fact indicates increase of hole density in Pd 4$$d$$-band. (3) 0.9 eV chemical shift was also observed in Pd $$L$$3 white line for Pd/Cu samples, which will affect the quality of the Li/Pd/Cu target due to the formation of PdH$$_{x}$$ in palladium insert layer.

Journal Articles

Surficial chemical states of Li$$_{3}$$N synthesized on lithium target for boron neutron capture therapy

Ishiyama, Shintaro; Baba, Yuji; Fujii, Ryo*; Nakamura, Masaru*; Imahori, Yoshio*

Materials Transactions, 55(3), p.539 - 542, 2014/01

 Times Cited Count:2 Percentile:12.41(Materials Science, Multidisciplinary)

To remove high level of contaminants by O and C from Li$$_{3}$$N surface for BNCT target, high temperature thermal desorption was conducted up to 1123 K in ultra high vacuum and the following results were derived; (1) During thermal desorption up to 1023 K, typical three peaks of vacuum pressure disturbance due to vaporization of contaminants were observed in vacuum pressure-temperature curve. (2) Over-layered contaminants with high melting temperature below 1023 K on Li$$_{3}$$N surface is completely removed by high temperature thermal desorption up to 1123 K in ultra high vacuum. (3) From these desorption results, it is suggested that these contaminants corresponding to these vaporization peaks are H$$_{2}$$O and Li compounds with high melting temperature below 1023 K, of which LiOH and Li$$_{2}$$CO$$_{3}$$ were synthesized by decomposition process of Li$$_{3}$$N with residual H$$_{2}$$O and CO$$_{2}$$ in low temperature.

Journal Articles

Low temperature and pressure synthesis of lithium-nitride compound with H$$_{2}$$O addition on lithium target for BNCT

Ishiyama, Shintaro; Baba, Yuji; Fujii, Ryo*; Nakamura, Masaru*; Imahori, Yoshio*

Materials Transactions, 54(12), p.2233 - 2237, 2013/12

 Times Cited Count:4 Percentile:27.81(Materials Science, Multidisciplinary)

Low temperature synthesis of lithium-nitride compound was conducted on the lithium target for BNCT by N$$_{2}$$/H$$_{2}$$O mixing gas squirt in ultra high vacuum chamber, and the following results were derived; (1) Lithium-nitride compound was synthesized on lithium target under 101.3 PaN$$_{2}$$ gas squirt at room temperature and 1$$times$$ 10$$^{-8}$$ Pa in ultra high vacuum chamber. (2) Remarkable contamination by O and C was observed on the lithium-nitride compound synthesized by 13.3 $$sim$$ 80 Pa/1.33 $$sim$$ 4.7 Pa N$$_{2}$$/H$$_{2}$$O mixing gas squirt. (3) No contamination and synthesis of Li-N compound was observed at 0.013 $$sim$$ 0.027 Pa/0 $$sim$$ 0.005 Pa N$$_{2}$$/H$$_{2}$$O squirt. (4) Contamination by O and C is enhanced with excessive addition of over 1.33 Pa H$$_{2}$$O addition.

Journal Articles

Thermal stability of BNCT neutron production target synthesized by ${it in-situ}$ lithium deposition and ion implantation

Ishiyama, Shintaro; Baba, Yuji; Fujii, Ryo*; Nakamura, Masaru*; Imahori, Yoshio*

Nihon Kinzoku Gakkai-Shi, 77(11), p.509 - 513, 2013/11

 Times Cited Count:1 Percentile:10.56(Metallurgy & Metallurgical Engineering)

To testify thermal stability of the BNCT neutron target synthesized by ${it in-situ}$ lithium deposition and ion implantation, laser heating test of the Li$$_{3}$$N/Li/Cu tri-layered target was conducted in high vacuum chamber of 10$$^{-6}$$ Pa and thermal stability of the tri-layered target was characterized by X-ray photoelectron spectroscopy. Following conclusions were derived; (1) The Li$$_{3}$$N/Li/Cu tri- layered target with very low oxide and carbon contamination was synthesized by ${it in-situ}$ lithium deposition and ion implantation techniques without H$$_{2}$$O and O$$_{2}$$ additions (2) The starting temperature of evaporation of the Li$$_{3}$$N/Li/Cu tri-layered target increased by 120 K compared to that of the Li/Cu target and (3) frequent repair synthesis of the damaged Li$$_{3}$$N/Li/Cu tri-layered target caused by evaporation is possible.

Journal Articles

Thermal stability of BNCT neutron production target synthesized by ${it in-situ}$ lithium deposition and ion implantation

Ishiyama, Shintaro; Baba, Yuji; Fujii, Ryo*; Nakamura, Masaru*; Imahori, Yoshio*

Materials Transactions, 54(9), p.1760 - 1764, 2013/09

 Times Cited Count:4 Percentile:27.81(Materials Science, Multidisciplinary)

Li$$_{3}$$N synthesis on Li deposition layer was conducted without H$$_{2}$$O and O$$_{2}$$ by ${it in-situ}$ lithium deposition in high vacuum chamber of 10$$^{-6}$$ Pa and ion implantation techniques and the thermo-chemical stability of the Li$$_{3}$$N/Li/Cu tri-layered target under laser heating and air exposure was characterized by X-ray photoelectron spectroscopy. Following conclusions were derived; (1) Li$$_{3}$$N/Li/Cu tri- layered target with very low oxide and carbon contamination was synthesized by ${it in-situ}$ lithium deposition and ion implantation techniques without H$$_{2}$$O and O$$_{2}$$ additions and frequent synthesis of the target is possible. (2) The evaporating temperature of Li deposited layer increased by 120 K after forming the Li$$_{3}$$N layer on the surface of Li. (3) Remarkable oxidation and carbon contamination were observed on the surfaces of Li/Cu and Li$$_{3}$$N/Li/Cu after air exposure and these contaminated compositions formed on the surface of Li$$_{3}$$N/Li/Cu was not removed by Ar heavy sputtering.

Journal Articles

Direct synthesis of Li$$_{3}$$N thin layer on lithium target surface for BNCT in N$$_{2}$$ gaseous conditions

Ishiyama, Shintaro; Baba, Yuji; Fujii, Ryo*; Nakamura, Masaru*; Imahori, Yoshio*

Materials Transactions, 54(9), p.1765 - 1769, 2013/09

 Times Cited Count:4 Percentile:27.81(Materials Science, Multidisciplinary)

To prevent vaporization damage of BNCT (Boron Neutron Capture Therapy) lithium target during operation, direct synthesis of Li$$_{3}$$N thin layer on lithium target surface was demonstrated in 0.1 MPa N$$_{2}$$ gas at temperature below 548 K and the following conclusions were derived; (1)Synthesis of Li$$_{3}$$N thin layer on lithium surface was confirmed after nitridation at 276$$sim$$548 K with surface contamination by oxygen and carbon. (2) Rapid nitridation over 1$$sim$$5wt.%/min was observed above Li melting temperature, whereas slow reaction under 0.02$$sim$$0.5wt.%/min below melting temperature. (3) During nitridation, removal of oxygen contamination on Li$$_{3}$$N thin layer is taken place by nitrogen below Li melting temperature.

Journal Articles

Synthesis of lithium nitride for neutron production target of BNCT by ${it in situ}$ lithium deposition and ion implantation

Ishiyama, Shintaro; Baba, Yuji; Fujii, Ryo*; Nakamura, Masaru*; Imahori, Yoshio*

Nuclear Instruments and Methods in Physics Research B, 293, p.42 - 47, 2012/12

 Times Cited Count:13 Percentile:69.26(Instruments & Instrumentation)

To achieve high performance of BNCT (Boron Neutron Capture Therapy) device, lithium nitride target for neutron production was synthesized by in-situ vacuum deposition and nitridation techniques. Following conclusions were derived; (1) Uniform lithium layer of a few hundreds nanometer was formed on Pd/Cu multilayer surface by ${it in situ}$ vacuum deposition technique using metallic lithium as a source material. (2) Lithium nitrides were formed by ${it in situ}$ nitridation by the implantation of low-energy nitrogen ions on the deposited lithium layer surface. The chemical states of the nitridated zone were close to the stoichiometric lithium nitride, Li$$_{3}$$N. (3) This nitridated zone formed on surface of four layered lithium target is stable for three months in air condition. The ${it in situ}$ nitridation is effective to protect lithium target from degradation by unfavourable reactions.

Journal Articles

In-situ vacuum deposition technique of lithium on neutron production target for BNCT

Ishiyama, Shintaro; Baba, Yuji; Fujii, Ryo*; Nakamura, Masaru*; Imahori, Yoshio*

Nuclear Instruments and Methods in Physics Research B, 288, p.18 - 22, 2012/10

To achieve high performance of BNCT (Boron Neutron Capture Therapy) device, lithium target for neutron production was redesigned, and the layered structures of the synthesized target were characterized. Following conclusions were derived; (1) Uniform lithium layers with the thickness from 1.6 nm to a few hundreds nanometer were formed on Pd/Cu multilayer surface by in-situ vacuum deposition technique using metallic lithium as a source material. (2) Re-deposition of lithium layer on Li surface can be achieved by in-situ vacuum deposition technique. (3) Small amount of water and carbonate was observed on the top surface of Li. But the thickness of the adsorbed layer was less than monolayer, which will not affect the quality of the Li target. (4) The formation of Pd-Li alloy layer was observed at the Pd and Li interface. The alloy layer would contribute to the stability of the Li layer.

Journal Articles

In-situ vacuum deposition technique of lithium on neutron production target for BNCT

Ishiyama, Shintaro; Baba, Yuji; Fujii, Ryo*; Nakamura, Masaru*; Imahori, Yoshio*

Nuclear Instruments and Methods in Physics Research B, 288, p.18 - 22, 2012/10

 Times Cited Count:12 Percentile:66.88(Instruments & Instrumentation)

For the purpose of avoiding the radiation blistering of the lithium target for neutron production in BNCT (Boron Neutron Capture Therapy) device, trilaminar Li target, of which palladium thin layer was inserted between cupper substrate and Li layer, was newly designed. In-situ vacuum deposition and electrolytic coating techniques were applied to validate the method of fabrication of the Li/Pd/Cu target, and the layered structures of the synthesized target were characterized. In-situ vacuum re-deposition technique was also established for repairing and maintenance for lithium target damaged. Following conclusions were derived; (1) Uniform lithium layers with the thickness from 1.6 nm to a few hundreds nanometer were formed on Pd/Cu multilayer surface by in situ vacuum deposition technique using metallic lithium as a source material. (2) Re-deposition of lithium layer on Li surface can be achieved by in situ vacuum deposition technique.

Journal Articles

The H-Invitational Database (H-InvDB); A Comprehensive annotation resource for human genes and transcripts

Yamasaki, Chisato*; Murakami, Katsuhiko*; Fujii, Yasuyuki*; Sato, Yoshiharu*; Harada, Erimi*; Takeda, Junichi*; Taniya, Takayuki*; Sakate, Ryuichi*; Kikugawa, Shingo*; Shimada, Makoto*; et al.

Nucleic Acids Research, 36(Database), p.D793 - D799, 2008/01

 Times Cited Count:51 Percentile:71.49(Biochemistry & Molecular Biology)

Here we report the new features and improvements in our latest release of the H-Invitational Database, a comprehensive annotation resource for human genes and transcripts. H-InvDB, originally developed as an integrated database of the human transcriptome based on extensive annotation of large sets of fulllength cDNA (FLcDNA) clones, now provides annotation for 120 558 human mRNAs extracted from the International Nucleotide Sequence Databases (INSD), in addition to 54 978 human FLcDNAs, in the latest release H-InvDB. We mapped those human transcripts onto the human genome sequences (NCBI build 36.1) and determined 34 699 human gene clusters, which could define 34 057 protein-coding and 642 non-protein-coding loci; 858 transcribed loci overlapped with predicted pseudogenes.

Journal Articles

Status of the ECR ion source for TRIAC

Nakanoya, Takamitsu; Matsuda, Makoto; Fujii, Yoshio*

Proceedings of 2nd Annual Meeting of Particle Accelerator Society of Japan and 30th Linear Accelerator Meeting in Japan, p.729 - 730, 2005/07

TRIAC (Tokai Radioactive Ion Accelerator Complex) facility can accelerate both radioactive and stable ion beams up to 1.1Mev/u. In this facility, an ECR ion source is used for production of stable ion beams. Stable ion beams are used mainly as a pilot beam for radioactive ion beam. ECR ion source is required to produce many kinds of ion species, not only gas state elements. So, we developed a high temperature oven for obtaining metal ion beams. This paper describes the design and detail of the oven and experimental results.

Journal Articles

Progress in physics and technology developments for the modification of JT-60

Tamai, Hiroshi; Matsukawa, Makoto; Kurita, Genichi; Hayashi, Nobuhiko; Urata, Kazuhiro*; Miura, Yushi; Kizu, Kaname; Tsuchiya, Katsuhiko; Morioka, Atsuhiko; Kudo, Yusuke; et al.

Plasma Science and Technology, 6(1), p.2141 - 2150, 2004/02

 Times Cited Count:2 Percentile:6.54(Physics, Fluids & Plasmas)

The dominant issue for the the modification program of JT-60 (JT-60SC) is to demonstrate the steady state reactor relevant plasma operation. Physics design on plasma parameters, operation scenarios, and the plasma control method are investigated for the achievement of high-$$beta$$. Engineering design and the R&D on the superconducting magnet coils, radiation shield, and vacuum vessel are performed. Recent progress in such physics and technology developments is presented.

Journal Articles

Reactivity estimation using digital nonlinear H$$_{infty}$$ estimator for VHTRC experiment

Suzuki, Katsuo; Nabeshima, Kunihiko; Yamane, Tsuyoshi; Fujii, Yoshio*

Nihon Genshiryoku Gakkai Wabun Rombunshi, 2(4), p.408 - 417, 2003/12

On-line and real-time estimation of time-varying reactivity in a nuclear reactor is necessary for early detection of reactivity anomaly and safe operation. Using a digital nonlinear H$$infty$$ estimator, an experiment of real-time dynamic reactivity estimation was carried out in the VHTRC of JAERI. Some technical issues of the experiment are described, such as reactivity insertion, data sampling frequency, anti-aliasing filter, experimental circuit and digitalizing nonlinear H$$infty$$ reactivity estimator, and so on. Then, we discussed the experimental results obtained by the digital nonlinear H$$infty$$ estimator with sampled data of the nuclear instrumentation signal for the power responses under various reactivity insertions. Good performances of estimated reactivity were observed, with almost no delay to the true reactivity and sufficient accuracy between 0.05cent and 0.1cent. From the results of the experiment, it is concluded that the digital nonlinear H$$infty$$ reactivity estimator can be applied as on-line real-time reactivity meter for actual nuclear plants.

Journal Articles

Objectives and design of the JT-60 superconducting tokamak

Ishida, Shinichi; Abe, Katsunori*; Ando, Akira*; Chujo, T.*; Fujii, Tsuneyuki; Fujita, Takaaki; Goto, Seiichi*; Hanada, Kazuaki*; Hatayama, Akiyoshi*; Hino, Tomoaki*; et al.

Nuclear Fusion, 43(7), p.606 - 613, 2003/07

no abstracts in English

Journal Articles

Objectives and design of the JT-60 superconducting tokamak

Ishida, Shinichi; Abe, Katsunori*; Ando, Akira*; Cho, T.*; Fujii, Tsuneyuki; Fujita, Takaaki; Goto, Seiichi*; Hanada, Kazuaki*; Hatayama, Akiyoshi*; Hino, Tomoaki*; et al.

Nuclear Fusion, 43(7), p.606 - 613, 2003/07

 Times Cited Count:33 Percentile:69.34(Physics, Fluids & Plasmas)

no abstracts in English

43 (Records 1-20 displayed on this page)