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Journal Articles

Magnetoelastic anisotropy in Heusler-type Mn$$_{2-delta}$$CoGa$$_{1+delta}$$ films

Kubota, Takahide*; Takano, Daichi*; Kota, Yohei*; Mohanty, S.*; Ito, Keita*; Matsuki, Mitsuhiro*; Hayashida, Masahiro*; Sun, M.*; Takeda, Yukiharu; Saito, Yuji; et al.

Physical Review Materials (Internet), 6(4), p.044405_1 - 044405_12, 2022/04

 Times Cited Count:1 Percentile:54.41(Materials Science, Multidisciplinary)

Journal Articles

Microstructures and interface magnetic moments in Mn$$_{2}$$VAl/Fe layered films showing exchange bias

Kubota, Takahide*; Shimada, Yusuke*; Tsuchiya, Tomoki*; Yoshikawa, Tomoki*; Ito, Keita*; Takeda, Yukiharu; Saito, Yuji; Konno, Toyohiko*; Kimura, Akio*; Takanashi, Koki*

Nanomaterials (Internet), 11(7), p.1723_1 - 1723_11, 2021/07

 Times Cited Count:2 Percentile:18.63(Chemistry, Multidisciplinary)

Journal Articles

Controlled growth of boron-doped epitaxial graphene by thermal decomposition of a B$$_{4}$$C thin film

Norimatsu, Wataru*; Matsuda, Keita*; Terasawa, Tomoo; Takata, Nao*; Masumori, Atsushi*; Ito, Keita*; Oda, Koji*; Ito, Takahiro*; Endo, Akira*; Funahashi, Ryoji*; et al.

Nanotechnology, 31(14), p.145711_1 - 145711_7, 2020/04

 Times Cited Count:6 Percentile:39.72(Nanoscience & Nanotechnology)

We show that boron-doped epitaxial graphene can be successfully grown by thermal decomposition of a boron carbide thin film, which can also be epitaxially grown on a silicon carbide substrate. The interfaces of B$$_{4}$$C on SiC and graphene on B$$_{4}$$C had a fixed orientation relation, having a local stable structure with no dangling bonds. The first carbon layer on B$$_{4}$$C acts as a buffer layer, and the overlaying carbon layers are graphene. Graphene on B$$_{4}$$C was highly boron doped, and the hole concentration could be controlled over a wide range of 2$$times$$10$$^{13}$$ to 2$$times$$10$$^{15}$$ cm$$^{-2}$$. Highly boron-doped graphene exhibited a spin-glass behavior, which suggests the presence of local antiferromagnetic ordering in the spin-frustration system. Thermal decomposition of carbides holds the promise of being a technique to obtain a new class of wafer-scale functional epitaxial graphene for various applications.

Journal Articles

Manipulation of saturation magnetization and perpendicular magnetic anisotropy in epitaxial Co$$_{x}$$Mn$$_{4-x}$$N films with ferrimagnetic compensation

Ito, Keita*; Yasutomi, Yoko*; Zhu, S.*; Nurmamat, M.*; Tahara, Masaki*; Toko, Kaoru*; Akiyama, Ryota*; Takeda, Yukiharu; Saito, Yuji; Oguchi, Tamio*; et al.

Physical Review B, 101(10), p.104401_1 - 104401_8, 2020/03

 Times Cited Count:14 Percentile:73.8(Materials Science, Multidisciplinary)

Journal Articles

Preferred site occupation of 3$$d$$ atoms in Ni$$_{x}$$Fe$$_{4-x}$$N (${it x}$ = 1 and 3) films revealed by X-ray absorption spectroscopy and magnetic circular dichroism

Takata, Fumiya*; Ito, Keita*; Takeda, Yukiharu; Saito, Yuji; Takanashi, Koki*; Kimura, Akio*; Suemasu, Takashi*

Physical Review Materials (Internet), 2(2), p.024407_1 - 024407_5, 2018/02

 Times Cited Count:14 Percentile:48.99(Materials Science, Multidisciplinary)

Journal Articles

Local electronic states of Fe$$_{4}$$N films revealed by X-ray absorption spectroscopy and X-ray magnetic circular dichroism

Ito, Keita*; Toko, Kaoru*; Takeda, Yukiharu; Saito, Yuji; Oguchi, Tamio*; Suemasu, Takashi*; Kimura, Akio*

Journal of Applied Physics, 117(19), p.193906_1 - 193906_6, 2015/05

 Times Cited Count:14 Percentile:52.58(Physics, Applied)

Journal Articles

X-ray magnetic circular dichroism for Co$$_{x}$$Fe$$_{4-x}$$N (x = 0, 3, 4) films grown by molecular beam epitaxy

Ito, Keita*; Sanai, Tatsunori*; Yasutomi, Yoko*; Zhu, S.-Y.*; Toko, Kaoru*; Takeda, Yukiharu; Saito, Yuji; Kimura, Akio*; Suemasu, Takashi*

Journal of Applied Physics, 115(17), p.17C712_1 - 17C712_3, 2014/05

 Times Cited Count:18 Percentile:60.54(Physics, Applied)

Oral presentation

New small sodium leak detection system, 2; An Experiment of moving fluid ionization detector and laser leak detector in fast breeder reactor Monju

Okazaki, Koki*; Naito, Susumu*; Nakayama, Kunihiko*; Makino, Shunichiro*; Shigeyama, Musashi*; Kuwako, Akira*; Izumi, Mikio*; Ito, Jun*; Okada, Hisashi*; Muto, Keitaro

no journal, , 

In fast breeder reactor (FBR), it is important to detect a small sodium leak surely for safety. As the coolant sodium used in FBR is low pressure, a small leak occurs from a crack before a pipe breaks, therefore it is possible to detect a sodium leak so as to shutdown a reactor before a pipe completely breaks. The sodium leaking from piping of cooling system reacts with oxygen etc. including with the ambient gas to form aerosols. In the second coolant system of the prototype liquid metal FBR Monju, the ambient air around piping is drawn into radiative ionization detector (RID). When sodium aerosols are detected by RID, chemical analysis of aerosols and the viewing of the leak point are carried out, then sodium leak is confirmed. As the signal of RID depends on temperature strongly and RID detects the aerosols which do not include sodium, the improvements of RID are demanded for reliability. Moving fluid ionization detector (MID) and laser leak detector (LLD) have been developed to improve these points. MID can reduce the dependence for temperature of the signal strength, and LLD can detect sodium atoms which are included in aerosols by means of laser-induced breakdown spectroscopy. An experiment was carried out for validating sodium leak detection system with MID and LLD under real environment installed in the second coolant system of Monju. In the experiments, sodium was not leaked, and ambient air around piping of the secondary coolant system was introduced through actual sampling line and measured by MID and LLD. In addition a sodium level in the ambient air was measured by means of ion chromatography. The experiment showed that the background signals of MID and LLD were stable and low and that the sodium level due to the background of salinity (NaCl) contained in the ambient air was lower than three orders of magnitude than the sodium level for small sodium leak. The plant applicability of MID and RID was validated by this experiment.

Oral presentation

Separation and recovery of platinum group metals from high-level radioactive liquid waste, 3; Adsorption properties by silica-supported adsorbent in radiation field

Ito, Tatsuya; Kim, S.-Y.*; Xu, Y.*; Hitomi, Keitaro*; Ishii, Keizo*; Nagaishi, Ryuji; Kimura, Takaumi

no journal, , 

no abstracts in English

Oral presentation

Separation and recovery of platinum group metals from high-level radioactive liquid waste, 5; Radiation effects on retention of PGMs in silica-supported adsorbent

Ito, Tatsuya; Kim, S.-Y.*; Xu, Y.*; Hitomi, Keitaro*; Ishii, Keizo*; Nagaishi, Ryuji; Kimura, Takaumi

no journal, , 

no abstracts in English

Oral presentation

Study on separation of platinum group metals from high level liquid waste using macroporous (MOTDGA-TOA)/SiO$$_{2}$$-P silica-based absorbent

Ito, Tatsuya; Kim, S.-Y.*; Xu, Y.*; Hitomi, Keitaro*; Ishii, Keizo*; Nagaishi, Ryuji; Kimura, Takaumi

no journal, , 

To research recovering of platinum group metals (PGMs) from high level liquid waste (HLLW) by macroporous silica-based adsorbent, the adsorbent of (MOTDGA-TOA)/SiO$$_{2}$$-P was developed by impregnating two extractants of N,N'-dimethyl-N,N'-di-n-octyl-thiodiglycolamide (MOTDGA) and tri-n-octylamine (TOA) into a silica/polymer composite support (SiO$$_{2}$$-P). The adsorbent showed good adsorption property for Pd(II). In addition, the combined use of MOTDGA and TOA improved adsorption of Ru(III) and Rh(III) better than the individual use of them. The usability of adsorbent in radiation fields was further confirmed by irradiation experiments. The adsorbent remained to have adsorption capability for PGMs at least adsorbed dose of 100 kGy, correspomding with one adsorbed by the adsorbent in their adsorption, and showed good retention capability for adsorbed Pd(II) even at the adsorbed dose of 800 kGy.

Oral presentation

Studies on PGMs adsorption and radiation resistance of macroporous (MOTDGA-TOA)/SiO$$_{2}$$-P silica-based absorbent under $$gamma$$-ray irradiation

Ito, Tatsuya; Nagaishi, Ryuji; Kim, S.-Y.*; Xu, Y.*; Hitomi, Keitaro*; Ishii, Keizo*; Kimura, Takaumi

no journal, , 

no abstracts in English

Oral presentation

Separation and recovery of platinum group metals from high-level radioactive liquid waste, 7; Comparing investigation of (Crea-TOA)/SiO$$_{2}$$-P and (MOTDGA-TOA)/SiO$$_{2}$$-P

Ito, Tatsuya; Kim, S.-Y.*; Xu, Y.*; Hitomi, Keitaro*; Ishii, Keizo*; Nagaishi, Ryuji; Kimura, Takaumi

no journal, , 

no abstracts in English

Oral presentation

Development of solidification techniques with minimised water content for secondary radioactive aqueous wastes in Fukushima, 1; Synthesis and evaluation of simulated wastes

Taniguchi, Takumi; Irisawa, Keita; Ito, Yuzuru; Namiki, Masahiro; Osugi, Takeshi; Abe, Tomohisa; Sato, Junya; Sakakibara, Tetsuro; Nakazawa, Osamu; Meguro, Yoshihiro; et al.

no journal, , 

no abstracts in English

Oral presentation

Development of a portable high-resolution gamma-ray spectrometer for nuclear facilities, 1; Research plan

Maeda, Shigetaka; Nogami, Mitsuhiro*; Ito, Chikara; Watanabe, Kenichi*; Hitomi, Keitaro*

no journal, , 

A portable high-resolution gamma-ray spectrometer for nuclear facilities is developing. The research plan will be outlined, and the applicability to OLGM for fast reactor fuel failure detection and the required performance will be reported.

Oral presentation

Development of a portable high-resolution gamma-ray spectrometers for nuclear facilities, 2; Long-term stability of TlBr Detector at room temperature

Nogami, Mitsuhiro*; Hitomi, Keitaro*; Ito, Chikara; Tsubakiyama, Kunimi*; Watanabe, Kenichi*; Maeda, Shigetaka

no journal, , 

While many studies have been conducted on improving energy resolution and increasing the volume of TlBr detectors, little evaluation has been made on long-term stability. Therefore, in this study, we evaluated the long-term stability of the TlBr detector when it was operated continuously for about 2000 hours, assuming application to an actual nuclear power plant.

Oral presentation

Development of a portable high-resolution gamma-ray spectrometer for nuclear facilities, 3; Evaluation of TlBr crystalline quality using neutron Bragg-dip imaging

Watanabe, Kenichi*; Tsubakiyama, Kunimi*; Hitomi, Keitaro*; Nogami, Mitsuhiro*; Ito, Chikara; Maeda, Shigetaka

no journal, , 

The crystallinity of TlBr crystals was evaluated using the neutron Bragg dip imaging method, which is one of the neutral diffraction methods, as a part of the study for improving the detector performance.

Oral presentation

A Comparison between neutron diffraction and EBSD images for a TlBr crystal

Watanabe, Kenichi*; Hitomi, Keitaro*; Nogami, Mitsuhiro*; Maeda, Shigetaka; Ito, Chikara; Tanno, Takashi; Onabe, Hideaki*

no journal, , 

TlBr is a compound semiconductor with a high atomic number, high density and a wide bandgap, and is being developed as a gamma-ray detector material that can be operated at room temperature and has high detection efficiency. There is neutron diffraction in order to establish a crystal quality evaluation method for improving the yield in device fabrication, but the facilities that can be implemented are limited to large facilities such as J-PARC. The Electron Backscatter Diffraction (EBSD) image, which is one of the electron beam diffractions, can be obtained with an electron microscope, but only the information on the crystal surface can be obtained. In this study, the crystal orientation image was acquired for the TlBr crystal by neutron Bragg dip imaging, which is one of the neutron diffractions, and EBSD. By comparing both images, the applicability to a simple EBSD crystal quality evaluation method was examined.

Oral presentation

Fabrication of 2-cm thick TlBr detectors

Hitomi, Keitaro*; Maeda, Shigetaka; Nogami, Mitsuhiro*; Ito, Chikara; Watanabe, Kenichi*

no journal, , 

A 2-cm thick pixelated TlBr detector was fabricated in this study. A 50-mm diameter TlBr crystal was grown by the Bridgman-Stockbarger method using zone-purified materials. A pixelated TlBr detector was fabricated from the grown crystal with the dimension of 20 mm $$times$$ 20 mm $$times$$ 20 mm. The planar cathode and pixelated anodes were constructed on the crystal by vacuum evaporation of Tl. The anode consisted of 16-pixel electrodes (3 mm $$times$$ 3 mm) surrounded by a guard ring. A charge-sensitive preamplifier was connected to a pixel electrode on the device. The output signals from the preamplifier were recorded with a digitizer. The acquired signal waveforms were analyzed with a PC event by event for obtaining pulse-height spectra. The cathode surface of the pixelated TlBr detector was irradiated with an Am-241 gamma-ray source at room temperature. The applied bias voltage to the cathode was 2000 V. A clear full-energy peak corresponding to 59.5-keV gamma rays was obtained from the detector. The clear full-energy peak of 59.5-keV gamma-ray was reflecting the good electron transport property of the TlBr crystal.

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