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Journal Articles

Discussion; Making databases of parameter values of radionuclide transfer in environment and application for biospheric dose assessment

Takahashi, Tomoyuki*; Uchida, Shigeo*; Takeda, Seiji; Nakai, Kunihiro*

KURNS-EKR-11, p.97 - 102, 2021/03

This paper outlines the status of IAEA database compilation for migration parameters depending elements in a biosphere such as soil-to-plant transfer factor and bioconcentration factor of marine products, and the status of utilization of the database in dose evaluation of radioactive waste disposal in Japan. Additionally, in the case of applying a new database to the dose evaluation for future radioactive waste disposal in a specific area. We summarized the opinions of specialists and result of general discussion about future strategies to make a new database for their parameters, perspectives to be considered in it, issues, etc.

Journal Articles

A Sensitive method for Sr-90 analysis by accelerator mass spectrometry

Sasa, Kimikazu*; Honda, Maki; Hosoya, Seiji*; Takahashi, Tsutomu*; Takano, Kenta*; Ochiai, Yuta*; Sakaguchi, Aya*; Kurita, Saori*; Satou, Yukihiko; Sueki, Keisuke*

Journal of Nuclear Science and Technology, 58(1), p.72 - 79, 2021/01

 Times Cited Count:1 Percentile:39.17(Nuclear Science & Technology)

Journal Articles

Giant spin hydrodynamic generation in laminar flow

Takahashi, Ryo*; Chudo, Hiroyuki; Matsuo, Mamoru; Harii, Kazuya*; Onuma, Yuichi*; Maekawa, Sadamichi; Saito, Eiji

Nature Communications (Internet), 11, p.3009_1 - 3009_6, 2020/06

 Times Cited Count:4 Percentile:63.95(Multidisciplinary Sciences)

Journal Articles

Depth profile and inventory of $$^{36}$$Cl in soil near the Fukushima Dai-ichi Nuclear Power Plant

Ota, Yuki*; Sueki, Keisuke*; Sasa, Kimikazu*; Takahashi, Tsutomu*; Matsunaka, Tetsuya*; Matsumura, Masumi*; Tosaki, Yuki*; Honda, Maki*; Hosoya, Seiji*; Takano, Kenta*; et al.

JAEA-Conf 2018-002, p.99 - 102, 2019/02

no abstracts in English

Journal Articles

Radiocarbon variations in tree rings since 1960 near the Tokai nuclear facility, Japan

Matsunaka, Tetsuya*; Sasa, Kimikazu*; Takahashi, Tsutomu*; Hosoya, Seiji*; Matsumura, Masumi*; Satou, Yukihiko; Shen, H.*; Sueki, Keisuke*

Nuclear Instruments and Methods in Physics Research B, 439, p.64 - 69, 2019/01

 Times Cited Count:2 Percentile:42.44(Instruments & Instrumentation)

no abstracts in English

Journal Articles

Vortex rectenna powered by environmental fluctuations

Lustikova, J.*; Shiomi, Yuki*; Yokoi, Naoto*; Kabeya, Noriyuki*; Kimura, Noriaki*; Ienaga, Koichiro*; Kaneko, Shinichi*; Okuma, Satoshi*; Takahashi, Saburo*; Saito, Eiji

Nature Communications (Internet), 9, p.4922_1 - 4922_6, 2018/11

 Times Cited Count:13 Percentile:78.13(Multidisciplinary Sciences)

Journal Articles

Control of Ga-oxide interlayer growth and Ga diffusion in SiO$$_{2}$$/GaN stacks for high-quality GaN-based metal-oxide-semiconductor devices with improved gate dielectric reliability

Yamada, Takahiro*; Watanabe, Kenta*; Nozaki, Mikito*; Yamada, Hisashi*; Takahashi, Tokio*; Shimizu, Mitsuaki*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; Watanabe, Heiji*

Applied Physics Express, 11(1), p.015701_1 - 015701_4, 2018/01

 Times Cited Count:21 Percentile:83.58(Physics, Applied)

A simple and feasible method for fabricating high-quality and highly reliable GaN-based metal-oxide-semiconductor (MOS) devices was developed on the basis of systematic physical and electrical characterizations. Chemical vapor deposition of SiO$$_{2}$$ films directly onto GaN substrates forming Ga-oxide interlayers was used to fabricate SiO$$_{2}$$/GaO$$_{x}$$/GaN stacked structures. Although well-behaved hysteresis-free GaN-MOS capacitors with extremely low interface state density below 10$$^{10}$$cm$$^{-2}$$eV$$^{-1}$$ were obtained by post-deposition annealing, Ga diffusion into overlying SiO$$_{2}$$ layers severely degraded the insulating property and dielectric breakdown characteristics of the MOS devices. However, this problem was found to be solved by employing rapid thermal processing, leading to superior performance of the GaN-MOS devices in terms of interface quality, insulating property and gate dielectric reliability.

Journal Articles

Generation of megahertz-band spin currents using nonlinear spin pumping

Watanabe, Shingo*; Hirobe, Daichi*; Shiomi, Yuki*; Iguchi, Ryo*; Daimon, Shunsuke*; Kameda, Mai*; Takahashi, Saburo*; Saito, Eiji

Scientific Reports (Internet), 7, p.4576_1 - 4576_6, 2017/07

 Times Cited Count:4 Percentile:28.18(Multidisciplinary Sciences)

Journal Articles

Radiocarbon variations since 1960 in tree rings around the nuclear facilities of the eastern Japan

Matsunaka, Tetsuya*; Sasa, Kimikazu*; Takahashi, Tsutomu*; Hosoya, Seiji*; Matsumura, Masumi*; Sueki, Keisuke*; Satou, Yukihiko

Dai-19-Kai AMS Shimpojiumu, 2016-Nendo "Jumoku Nenrin" Kenkyukai Kyodo Kaisai Shimpojiumu Hokokushu, p.76 - 79, 2017/06

To evaluate the radiological impact of the atmospheric $$^{14}$$C discharge from the Tokai nuclear facilities, a 80-year-old Japanese pine tree from Tokai, 1.8 km south-southwest of the Tokai Nuclear Power Plants (Tokai NPP and Tokai-2 NPP) and 1.4 km North-Northwest of the Tokai Reprocessing Plant (Tokai RP), was cored and each annual ring was measured for $$^{14}$$C. The $$^{14}$$C specific activities varied from 232.8 Bq kg$$^{-1}$$ C to 403.3Bq kg$$^{-1}$$ C in the tree rings formed during the periods 1954-2013. The specific activities in 1967-2010 are significantly elevated compared with the ambient background values, clearly indicating $$^{14}$$C discharges from the nuclear facilities during their normal operation. The excess $$^{14}$$C activities of 0.5-70.0 Bq kg$$^{-1}$$ C in 1970-2011 are positively correlated with the estimated annual $$^{14}$$C discharges of 0.1-1.2 TBq from Tokai NPP and Tokai-2 NPP with R$$^{2}$$ of 0.66 (n = 38). These activity values of $$<$$ 70.0 Bq kg$$^{-1}$$ C were corresponding to an additional annual effective dose of $$<$$ 3.9 uSv via the food ingestion pathway in the study location.

Journal Articles

Fabrication and magnetic control of Y$$_3$$Fe$$_5$$O$$_{12}$$ cantilevers

Seo, Y.-J.*; Harii, Kazuya; Takahashi, Ryo*; Chudo, Hiroyuki; Oyanagi, Koichi*; Qiu, Z.*; Ono, Takahito*; Shiomi, Yuki*; Saito, Eiji

Applied Physics Letters, 110(13), p.132409_1 - 132409_4, 2017/03

 Times Cited Count:12 Percentile:63.51(Physics, Applied)

We have fabricated ferrite cantilevers in which their vibrational properties can be controlled by external magnetic fields. Submicron-scale cantilever structures were made from Y$$_3$$Fe$$_5$$O$$_{12}$$ films by physical etching combined with the use of a focused ion beam milling technique. We found that the cantilevers exhibit two resonance modes which correspond to horizontal and vertical vibrations. Under external magnetic fields, the resonance frequency of the horizontal mode increases, while that of the vertical mode decreases, quantitatively consistent with our numerical simulation for magnetic forces. The changes in resonance frequencies with magnetic fields reach a few percent, showing that an efficient magnetic control of resonance frequencies was achieved.

Journal Articles

Theory of spin Hall magnetoresistance (SMR) and related phenomena

Chen, Y.-T.*; Takahashi, Saburo*; Nakayama, Hiroyasu*; Althammer, M.*; Goennenwein, S. T. B.*; Saito, Eiji; Bauer, G. E. W.*

Journal of Physics; Condensed Matter, 28(10), p.103004_1 - 103004_15, 2016/03

 Times Cited Count:57 Percentile:63.7(Physics, Condensed Matter)

We review the so-called spin Hall magnetoresistance (SMR) in bilayers of a magnetic insulator and a metal, in which spin currents are generated in the normal metal by the spin Hall effect. The associated angular momentum transfer to the ferromagnetic layer and thereby the electrical resistance is modulated by the angle between the applied current and the magnetization direction. The SMR provides a convenient tool to non-invasively measure the magnetization direction and spin-transfer torque to an insulator. We introduce the minimal theoretical instruments to calculate the SMR, i.e. spin diffusion theory and quantum mechanical boundary conditions. This leads to a small set of parameters that can be fitted to experiments. We discuss the limitations of the theory as well as alternative mechanisms such as the ferromagnetic proximity effect and Rashba spin-orbit torques, and point out new developments.

Journal Articles

Simulation of discharge in insulating gas from initial partial discharge to growth of a stepped leader using the percolation model

Sasaki, Akira; Kato, Susumu*; Takahashi, Eiichi*; Kishimoto, Yasuaki*; Fujii, Takashi*; Kanazawa, Seiji*

Japanese Journal of Applied Physics, 55(2), p.026101_1 - 026101_10, 2016/02

 Times Cited Count:2 Percentile:12.91(Physics, Applied)

A percolation model of discharge, which can reproduce stochastic behaviors of initial partial discharge to the growth of a stepped leader, is presented. The model uses macroscopic cells, from which a network of electric circuits is defined, and the spatial and temporal evolutions of the electric field and current in the discharge medium are calculated. For each cell, one of two states, either insulator or conductor, which corresponds to neutral gas or ionized plasmas, respectively, is decided. The decision is made on the basis of probability for each calculation cell at each time step, taking the effects of local electric field and current, which enhance ionization and sustain the discharge channel, respectively, into account. The stochastic behavior of discharge is discussed, in conjunction with the characteristic feature of ionization, that is, the ionization occurs not only ahead of the streamer tip where the electric field is enhanced but randomly in the discharge medium.

Journal Articles

Spin hydrodynamic generation

Takahashi, Ryo*; Matsuo, Mamoru; Ono, Masao; Harii, Kazuya; Chudo, Hiroyuki; Okayasu, Satoru; Ieda, Junichi; Takahashi, Saburo*; Maekawa, Sadamichi; Saito, Eiji

Nature Physics, 12, p.52 - 56, 2016/01

 Times Cited Count:65 Percentile:95.17(Physics, Multidisciplinary)

Journal Articles

Barnett effect in paramagnetic states

Ono, Masao; Chudo, Hiroyuki; Harii, Kazuya; Okayasu, Satoru; Matsuo, Mamoru; Ieda, Junichi; Takahashi, Ryo*; Maekawa, Sadamichi; Saito, Eiji

Physical Review B, 92(17), p.174424_1 - 174424_4, 2015/11

 Times Cited Count:19 Percentile:68.15(Materials Science, Multidisciplinary)

Journal Articles

Stabilization of a high-order harmonic generation seeded extreme ultraviolet free electron laser by time-synchronization control with electro-optic sampling

Tomizawa, Hiromitsu*; Sato, Takahiro*; Ogawa, Kanade*; Togawa, Kazuaki*; Tanaka, Takatsugu*; Hara, Toru*; Yabashi, Makina*; Tanaka, Hitoshi*; Ishikawa, Tetsuya*; Togashi, Tadashi*; et al.

High Power Laser Science and Engineering, 3, p.e14_1 - e14_10, 2015/04

 Times Cited Count:4 Percentile:29.28(Optics)

no abstracts in English

Journal Articles

The Spin state of iron in Fe$$^{3+}$$-bearing Mg-perovskite and its crystal chemistry at high pressure

Mashimo, Izumi*; Otani, Eiji*; Hirao, Naohisa*; Mitsui, Takaya; Masuda, Ryo*; Seto, Makoto*; Sakai, Takeshi*; Takahashi, Suguru*; Nakano, Satoshi*

American Mineralogist, 99(8-9), p.1555 - 1561, 2014/08

 Times Cited Count:6 Percentile:26.07(Geochemistry & Geophysics)

Journal Articles

Anomalous temperature dependence of current-induced torques in CoFeB/MgO heterostructures with Ta-based underlayers

Kim, J.*; Sinha, J.*; Mitani, Seiji*; Hayashi, Masamitsu*; Takahashi, Saburo*; Maekawa, Sadamichi; Yamanouchi, Michihiko*; Ono, Hideo*

Physical Review B, 89(17), p.174424_1 - 174424_8, 2014/05

 Times Cited Count:81 Percentile:94.83(Materials Science, Multidisciplinary)

We have studied the underlayer thickness and temperature dependencies of the current-induced effective field in CoFeB/MgO heterostructures with Ta-based underlayers. The underlayer thickness at which the effective field saturates is found to be different between the two orthogonal components of the effective field; i.e., the dampinglike term tends to saturate at a smaller underlayer thickness than the fieldlike term. For large underlayer thickness films in which the effective field saturates, we find that the measurement temperature significantly influences the size of the effective field. A striking difference is found in the temperature dependence of the two components: the dampinglike term decreases whereas the fieldlike term increases with increasing temperature. Using a simple spin diffusion-spin transfer model, we find that all of these results can be accounted for provided the real and imaginary parts of an effective spin mixing conductance are negative. These results imply that either spin transport in this system is different from conventional metallic interfaces or effects other than spin diffusion into the magnetic layer need to be taken into account in order to model the system accurately.

Journal Articles

Thermal engineering of non-local resistance in lateral spin valves

Kasai, Shinya*; Hirayama, Yusuke*; Takahashi, Yukiko*; Mitani, Seiji*; Hono, Kazuhiro*; Adachi, Hiroto; Ieda, Junichi; Maekawa, Sadamichi

Applied Physics Letters, 104(16), p.162410_1 - 162410_4, 2014/04

 Times Cited Count:9 Percentile:43.85(Physics, Applied)

Journal Articles

A Percolation model of the streamer discharges

Sasaki, Akira; Kato, Susumu*; Takahashi, Eiichi*; Kanazawa, Seiji*

JPS Conference Proceedings (Internet), 1, p.015029_1 - 015029_4, 2014/03

Although streamer discharges have long been studied, the mechanism of sudden formation of the complex discharge path has not been fully understood. We show that a simulation based on the percolation model reproduces such development of the streamer. In the model, the discharge medium is divided into cells and is considered to form an electrical circuit network, which is used to calculate the current. In contrast to the characteristic feature of a single electron avalanche is explained by the Townsend theory, when the size of the system becomes greater, random formation of the avalanche in the medium and connection between them determines the propagation of the steamer, which is analyzed using the percolation model. Figure shows the simulated discharge from the initial pre-discharge activity near the electrode to rapid growth of the stepped leader, which causes breakdown.

Journal Articles

Spin mixing conductance at a well-controlled platinum/yttrium iron garnet interface

Qiu, Z.*; Ando, Kazuya*; Uchida, Kenichi*; Kajiwara, Yosuke*; Takahashi, Ryo*; Nakayama, Hiroyasu*; An, Toshu*; Fujikawa, Yasunori*; Saito, Eiji

Applied Physics Letters, 103(9), p.092404_1 - 092404_4, 2013/08

 Times Cited Count:97 Percentile:95.88(Physics, Applied)

A platinum (Pt)/yttrium iron garnet (YIG) bilayer system with a well-controlled interface has been developed; spin mixing conductance at the Pt/YIG interface has been studied. A clear interface with good crystal perfection is experimentally demonstrated to be one of the important factors for an ultimate spin mixing conductance. The spin mixing conductance is obtained to be 1.3$$times$$10$$^{18}$$m$$^{-2}$$ at the well-controlled Pt/YIG interface, which is close to a theoretical prediction.

146 (Records 1-20 displayed on this page)