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論文

Application of diffusive gradients in thin films (DGT) for the dynamic speciation of radioactive cesium in Fukushima Prefecture, Japan

田中 琢朗*; 福岡 将史*; 戸田 賀奈子*; 中西 貴宏; 寺島 元基; 藤原 健壮; 庭野 佑真*; 加藤 弘亮*; 小林 奈通子*; 田野井 慶太朗*; et al.

ACS ES&T Water (Internet), 4(8), p.3579 - 3586, 2024/08

https://doi.org/10.1021/acsestwater.4c00453

Radioactive cesium released by the Fukushima Daiichi Nuclear Power Plant accident in March 2011 remains in the forest environment and is being transported to the ocean via residential areas by runoff into river systems. Most of the $$^{137}$$Cs in river water exists as suspended forms, being strongly fixed by micaceous clay minerals. If this fraction can change its form into dissolved forms, this results in additional input of bioavailable $$^{137}$$Cs. In this study, in-situ sampling of $$^{137}$$Cs at multiple rivers in Fukushima Prefecture was conducted using the DGT (diffusive gradient in thin film) devices to investigate the dynamics of radioactive cesium in river environments. At almost all sampling points, the DGT $$^{137}$$Cs concentrations exceeded dissolved $$^{137}$$Cs concentrations, revealing the existence of a flux from the suspended to the dissolved forms. This additional input was found to have higher $$^{137}$$Cs/ $$^{133}$$Cs ratios, compared those of Cs in the dissolved form. This study demonstrates that the bioavailability of $$^{137}$$Cs can be underestimated by assessing only the dissolved form due to $$^{137}$$Cs flux from the suspended particles likely caused by their dissolution.

論文

Analyses of hierarchical structures in SBR rubber by using contrast-variation SANS; Effects of a silane coupling agent

中西 洋平*; 柴田 基樹*; 澤田 諭*; 近藤 寛朗*; 元川 竜平; 熊田 高之; 山本 勝宏*; 三田 一樹*; 宮崎 司*; 竹中 幹人*

Polymer, 306, p.127209_1 - 127209_7, 2024/06

https://doi.org/10.1016/j.polymer.2024.127209
 被引用回数：2 パーセンタイル：56.40(Polymer Science)

Adding silane coupling agents to rubber/silica particles systems improves their mechanical properties and the dispersion of the particles. The improvement is believed to be attributed to the enhanced adsorption of rubber molecules on the surface of silica particles by the silane coupling agent. However, the enhancement of the adsorption by silane coupling agent has not been clarified quantitatively yet. In this study, we have investigated the difference in (i) the adsorption of rubber on silica surfaces and (ii) the aggregation of silica particles in rubber/silica particle systems with and without silane coupling agents by using contrast variation neutron scattering (CV-SANS). The CVSANS results quantitatively clarified the adsorption layer's thickness and the degree of aggregation for both systems. In the case of the system without silane coupling agents, the adsorption layers do not exist around the particles, and the particles tend to aggregate. On the other hand, the adsorption layers of about 5.3 nm are formed on the surface of the particles in the system with silane coupling agents, and the addition of silane coupling agents suppressed the aggregation.

論文

Magnetic excitation in the $$S$$=1/2 Ising-like antiferromagnetic chain CsCoCl$$_{3}$$ in longitudinal magnetic fields studied by high-field ESR measurements

木村 尚次郎*; 大西 弘明; 奥西 巧一*; 赤木 暢*; 鳴海 康雄*; 萩原 政幸*; 金道 浩一*; 菊池 彦光*

Journal of the Physical Society of Japan, 92(9), p.094701_1 - 094701_9, 2023/09

https://doi.org/10.7566/JPSJ.92.094701
 被引用回数：0 パーセンタイル：0.00(Physics, Multidisciplinary)

High-field electron spin resonance (ESR) measurements were performed on the $$S$$=1/2 Ising-like antiferromagnetic chain CsCoCl$$_{3}$$ in the frequency range up to 4.4THz and magnetic fields for $$H parallel c$$ up to 53T. We observed softening of the spinon excitation, which drives the spin chain into the quantum critical state at the critical field $$H_{c}$$=33.0T. Above $$H_{c}$$, we observed the string excitation at the wave number $$q$$=$$pi$$, which is characteristic of the $$S$$=1/2 spin chain in the quantum critical state in the magnetic fields. We also observed a crossover of the string excitation to the magnon bound state above the saturation fields $$H_{s}$$=43.9T upon increasing the magnetic fields. Finally, we discuss how the string excitation and magnon bound state can be excited by the electric dipole transition due to spin quadrupolar resonance.

論文

Low temperature behavior of itinerant ferromagnet realized in extended Nagaoka mechanism

大西 弘明; 宮下 精二*

JPS Conference Proceedings (Internet), 38, p.011157_1 - 011157_6, 2023/05

https://doi.org/10.7566/JPSCP.38.011157

We have proposed a Hubbard model which exhibits itinerant ferromagnetism by extending the model of Nagaoka ferromagnetism. In the present work, we confirm that the idea of the realization of itinerant ferromagnetism works in two- and three-dimensional lattices as well as a one-dimensional lattice which we studied previously. We also investigate the temperature dependence of the magnetic ordering and present a magnetic phase diagram in the space of the temperature and the chemical potential. In the obtained phase diagram, we find a V-shape structure for the magnetic ordering near a quantum phase transition. Besides, we find an additional peak exhibiting a dome structure. Temperature dependences of related spin correlation functions are studied in detail.

論文

Finite-temperature properties of extended Nagaoka ferromagnetism; Ordering processes and precursor of a quantum phase transition between itinerant ferromagnetic and Mott antiferromagnetic states

大西 弘明; 宮下 精二*

Physical Review B, 106(13), p.134436_1 - 134436_13, 2022/10

https://doi.org/10.1103/PhysRevB.106.134436
 被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)

We study finite-temperature properties of a Hubbard model including sites of a particle bath which was proposed as a microscopic model to show itinerant ferromagnetism at finite electron density. We use direct numerical methods, such as exact diagonalization and random vector methods. The temperature dependence of quantities is surveyed in the full range of the temperature. We find that the specific heat has several peaks, which correspond to ordering processes in different energy scales. In particular, magnetic correlations develop at very low temperature. The system exhibits an itinerant ferromagnetic state or an antiferromagnetic state of the Mott insulator depending on the chemical potential of the particle bath and the Coulomb interaction. From a microscopic viewpoint, the competition between these two types of magnetic states causes a peculiar ordering process of local spin correlations. Some local ferromagnetic correlations are found to be robust, which indicates that the ferromagnetic correlation originates from the motion of itinerant electrons in a short-range cluster.

論文

Sodium-cooled Fast Reactors

大島 宏之; 森下 正樹*; 相澤 康介; 安藤 勝訓; 芦田 貴志; 近澤 佳隆; 堂田 哲広; 江沼 康弘; 江連 俊樹; 深野 義隆; et al.

Sodium-cooled Fast Reactors; JSME Series in Thermal and Nuclear Power Generation, Vol.3, 631 Pages, 2022/07

https://shop.elsevier.com/books/sodium-cooled-fast-reactors/morishita/978-0-12-824076-2

ナトリウム冷却高速炉(SFR: Sodium-cooled Fast Reactor)の歴史や、利点、課題を踏まえた安全性、設計、運用、メンテナンスなどについて解説する。AIを利用した設計手法など、SFRの実用化に向けた設計や研究開発についても述べる。

論文

Excitation and transport of bound magnon clusters in frustrated ferromagnetic chain

大西 弘明

Journal of Physics; Conference Series, 2207, p.012045_1 - 012045_6, 2022/03

https://doi.org/10.1088/1742-6596/2207/1/012045

By exploiting density-matrix renormalization group methods, we study magnetic and transport properties of a frustrated quantum spin chain with ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor exchange interactions in an applied magnetic field. In high magnetic fields, there appear a series of spin multipole liquid ground states such as quadrupole, octupole, and hexadecapole, which are two-, three-, and four-magnon bound states, respectively. Since the low-energy excitation is governed by multi-magnon bound states, we envisage that bound magnon clusters would carry spin current. We will report detailed analyses of multipole excitation spectra and current correlation functions, and discuss how the magnon clusters contribute to the transport.

論文

Optical selection rules of the magnetic excitation in the $$S$$ = $$frac{1}{2}$$ one-dimensional Ising-like antiferromagnet BaCo$$_{2}$$V$$_{2}$$O$$_{8}$$

木村 尚次郎*; 大西 弘明; 奥谷 顕*; 赤木 暢*; 鳴海 康雄*; 萩原 政幸*; 奥西 巧一*; 金道 浩一*; He, Z.*; 谷山 智康*; et al.

Physical Review B, 105(1), p.014417_1 - 014417_9, 2022/01

https://doi.org/10.1103/PhysRevB.105.014417
 被引用回数：4 パーセンタイル：34.41(Materials Science, Multidisciplinary)

In this study, we clarify the selection rules of optical transitions from the ground state to the magnetic excited states in the quasi-one-dimensional quantum Ising-like antiferromagnet BaCo$$_{2}$$V$$_{2}$$O$$_{8}$$ with spin $$S$$ = $$frac{1}{2}$$ using the high-field electron spin resonance measurement with illuminating polarized electromagnetic waves. We demonstrate that the unconventional magnetic excitation via the pair creation of quasipaticles at wave numbers $$q_{z}=pi/2$$ and $$pi$$ in the field-induced quantum critical state can couple with both oscillating magnetic and electric fields. Our density matrix renormalization group calculations indicate that the observed selection rules can be explained by two- and four-fold periodical spin interactions, originating from the screw chain structure in BaCo$$_{2}$$V$$_{2}$$O$$_{8}$$, in addition to the magnetoelectric coupling between spins and electric dipoles.

論文

Spin excitations of the $$S$$=1/2 one-dimensional Ising-like antiferromagnet BaCo$$_{2}$$V$$_{2}$$O$$_{8}$$ in transverse magnetic fields

奥谷 顕*; 大西 弘明; 木村 尚次郎*; 竹内 徹也*; 木田 孝則*; 森 道康; 三宅 厚志*; 徳永 将史*; 金道 浩一*; 萩原 政幸*

Journal of the Physical Society of Japan, 90(4), p.044704_1 - 044704_9, 2021/04

https://doi.org/10.7566/JPSJ.90.044704
 被引用回数：4 パーセンタイル：38.65(Physics, Multidisciplinary)

The high-field multifrequency electron spin resonance (ESR), the magnetization, and the specific heat of single crystals of BaCo$$_{2}$$V$$_{2}$$O$$_{8}$$ (a quasi-one-dimensional Ising-like antiferromagnet with $$S=1/2$$) were measured in two different transverse magnetic fields: $$H parallel [100]$$ and $$H parallel [110]$$. A softening of the lowest ESR mode was observed near the saturation field of the magnetization around 40 T in $$H parallel [110]$$, whereas it occurs around 10 T in $$H parallel [100]$$, far below the saturation field. These observations were reproduced by numerical calculations using the density-matrix renormalization group methods, including the staggered magnetic fields induced by a uniform external magnetic field and the interchain magnetic exchange interaction. We found that the directional dependence of the lowest mode originates mainly from the remarkable angular dependence of the induced magnetic field. The interchain interaction is also quantitatively important for reproducing the experimental results. The directional dependence of the lowest mode is demonstrated by the particle-hole excitation of spinons using the Jordan-Wigner transformation.

論文

Repeatability and reproducibility of measurements of low dissolved radiocesium concentrations in freshwater using different pre-concentration methods

栗原 モモ*; 保高 徹生*; 青野 辰雄*; 芦川 信雄*; 海老名 裕之*; 飯島 健*; 石丸 圭*; 金井 羅門*; 苅部 甚一*; 近内 弥恵*; et al.

Journal of Radioanalytical and Nuclear Chemistry, 322(2), p.477 - 485, 2019/11

https://doi.org/10.1007/s10967-019-06696-2
 被引用回数：5 パーセンタイル：34.09(Chemistry, Analytical)

福島県の淡水に含まれる低レベル溶存態放射性セシウム濃度の測定に関する繰り返し精度と再現精度を評価した。21の実験施設が5つの異なる前濃縮法(プルシアンブルー含浸フィルターカートリッジ,リンモリブデン酸アンモニウム共沈,蒸発,固相抽出ディスク、およびイオン交換樹脂カラム)によって10L試料3検体を前濃縮し、放射性セシウム濃度を測定した。全$$^{137}$$Cs濃度測定結果のzスコアは$$pm$$2以内で、手法間の誤差は小さいことが示された。一方で、各実験施設内の相対標準偏差に比べて、施設間の相対標準偏差は大きかった。

論文

Magnetic excitations and transport properties in frustrated ferromagnetic chain

大西 弘明

Journal of Magnetism and Magnetic Materials, 479, p.88 - 90, 2019/06

https://doi.org/10.1016/j.jmmm.2019.02.006
 被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)

In a spin nematic state of a spin-1/2 frustrated ferromagnetic chain, low-energy excitations are governed by bound magnons, so that bound magnons carry spin current and thermal current. Regarding magnetic excitations, we find gapless longitudinal and gapped transverse spin excitation spectra, in accordance with quasi-long-range longitudinal and short-range transverse spin correlations, respectively, while we observe gapless quadrupole excitations, signaling quasi-long-range quadrupole correlations. In the present work, we investigate spin and thermal transport properties by exploiting numerical methods, such as exact diagonalization and density-matrix renormalization group. We will discuss the effects of bound magnon propagation in spin and thermal transport, based on detailed analyses of current-current correlation functions in the spin nematic ground state, and temperature and field dependencies of the spin Drude weight and the thermal Drude weight.

論文

第1分科会の質疑・討論

中西 宏晃; 仲宗根 卓*

国際法外交雑誌, 117(3), p.642 - 643, 2018/11

国際法学会2018年度(第121年次)研究大会第1分科会「核兵器不拡散条約(NPT)採択50年と核軍縮」の質疑・討論の要旨

論文

二国間原子力協力協定に係る昨今の米国政権の見解について

田崎 真樹子; 玉井 広史; 清水 亮; 木村 隆志; 北出 雄大; 中西 宏晃; 須田 一則

日本核物質管理学会第39回年次大会論文集(インターネット), 7 Pages, 2018/11

米国が他国と平和目的の原子力協力を行う上では、米国原子力法(AEA)に基づき、原則として9つの核不拡散要件を盛り込んだ二国間原子力協力協定(NCA)を締結する必要がある。本稿では、2018年7月末時点での米/サウジアラビアNCAに係る交渉と、2018年5月に署名された米/英、及び米/メキシコNCA等を例示し、昨今の米国のNCAに係る見解及び将来展望を考察した。

論文

国レベルコンセプト(SLC)の全体像の調査結果の概要

木村 隆志; 田崎 真樹子; 北出 雄大; 清水 亮; 玉井 広史; 中西 宏晃; 須田 一則

日本核物質管理学会第39回年次大会論文集(インターネット), 5 Pages, 2018/11

本報告では、IAEAが開発・実施している国レベルコンセプト(SLC)の調査結果の概要、及び主にSLCの下にてIAEAによる拡大結論の導出を継続することの重要性について国内原子力事業者の理解を促進するために報告する。

論文

国際原子力機関の拡大結論取得に係る加盟国の傾向の分析; 拡大結論の取得可能条件の抽出

中西 宏晃; 木村 隆志; 清水 亮; 北出 雄大; 田崎 真樹子; 玉井 広史; 須田 一則

日本核物質管理学会第39回年次大会論文集(インターネット), 9 Pages, 2018/11

本研究は、国際原子力機関(IAEA)が加盟国に拡大結論を下すための条件を抽出するために、拡大結論を取得した及び取得していない加盟国の傾向の比較検討を行うものである。

論文

「地域保障措置」の設立に係る要素の考察

北出 雄大; 玉井 広史; 田崎 真樹子; 清水 亮; 木村 隆志; 中西 宏晃; 須田 一則

日本核物質管理学会第39回年次大会論文集(インターネット), 9 Pages, 2018/11

「地域保障措置」は既存のIAEA保障措置を強化する手段の1つと考えられ、2000年以降のNPT運用検討会議ではその重要性に言及し、また2011年以降のNSGガイドラインは原子力資機材受領国に対する保障措置の条件として「地域保障措置」も掲げている。本研究は、代表的な「地域保障措置」として機能しているEURATOM及びABACCの事例に基づき、「地域保障措置」の設立に係る要素について検討する。

論文

Electrochemical reaction mechanisms under various charge-discharge operating conditions for Li$$_{1.2}$$Ni$$_{0.13}$$Mn$$_{0.54}$$Co$$_{0.13}$$O$$_{2}$$ in a lithium-ion battery

小西 宏明*; 平野 辰巳*; 高松 大郊*; 軍司 章*; Feng, X.*; 古月 翔*; 奥村 壮文*; 寺田 尚平*; 田村 和久

Journal of Solid State Chemistry, 262, p.294 - 300, 2018/06

https://doi.org/10.1016/j.jssc.2018.03.028
 被引用回数：10 パーセンタイル：47.92(Chemistry, Inorganic & Nuclear)

Li$$_{1.2}$$Ni$$_{0.13}$$Mn$$_{0.54}$$Co$$_{0.13}$$O$$_{2}$$正極の充電過程において、各SOCでの電極電位は、放電過程より高い。この機構を明らかにするために、様々なSOCにおいて電気化学測定、XRD, XAFS測定を行った。その結果、Li$$_{1.2}$$Ni$$_{0.13}$$Mn$$_{0.54}$$Co$$_{0.13}$$O$$_{2}$$の格子状数や遷移金属の酸化状態が異なっていることが分かった。また、Li$$_{1.2}$$Ni$$_{0.13}$$Mn$$_{0.54}$$Co$$_{0.13}$$O$$_{2}$$中に、LiNi$$_{0.33}$$Mn$$_{0.33}$$Co$$_{0.33}$$O$$_{2}$$やLi$$_{2}$$MnO$$_{3}$$に類似した構造が存在することも明らかになった。

論文

Dynamical quadrupole structure factor of frustrated ferromagnetic chain

大西 弘明

Physica B; Condensed Matter, 536, p.346 - 349, 2018/05

https://doi.org/10.1016/j.physb.2017.10.056
 被引用回数：2 パーセンタイル：9.03(Physics, Condensed Matter)

In a spin-1/2 $$J_{1}$$-$$J_{2}$$ Heisenberg chain with ferromagnetic $$J_{1}$$ and antiferromagnetic $$J_{2}$$, the ground state in high magnetic fields is a quadrupole state, the so-called spin nematic state. To understand the properties of the spin nematic state from the viewpoint of excitation dynamics, we have studied dynamical spin structure factors by density-matrix renormalization group methods. In the spin nematic regime, we find gapless longitudinal and gapped transverse spin excitation spectra, in accordance with quasi-long-ranged longitudinal and short-ranged transverse spin correlations, respectively. These features can be examined by inelastic neutron scattering experiments. However, they are indirect evidence for the spin nematic state. Here, we proceed to analyze dynamical quadrupole structure factors to clarify excitation dynamics in the quadrupole channel. We observe gapless excitations at $$q$$=$$pi$$, signaling quasi-long-ranged antiferro-quadrupole correlations. Information of spectral intensity distribution would be useful to discuss how we can detect the spin nematic state directly by experiments.

論文

Mechanisms responsible for two possible electrochemical reactions in Li$$_{1.2}$$Ni$$_{0.13}$$Mn$$_{0.54}$$Co$$_{0.13}$$O$$_{2}$$ used for lithium ion batteries

小西 宏明*; 平野 辰巳*; 高松 大郊*; 軍司 章*; Feng, X.*; 古月 翔*; 奥村 壮文*; 寺田 尚平*; 田村 和久

Journal of Solid State Chemistry, 258, p.225 - 231, 2018/02

https://doi.org/10.1016/j.jssc.2017.10.024
 被引用回数：9 パーセンタイル：44.23(Chemistry, Inorganic & Nuclear)

リチウムイオン電池の正極材料であるLi$$_{1.2}$$Ni$$_{0.13}$$Mn$$_{0.54}$$Co$$_{0.13}$$O$$_{2}$$について、充放電過程における構造変化について調べた。実験結果から、充電過程ではSOCが大きくなるとともに、Li$$_{2}$$MnO$$_{3}$$,LiNi$$_{0.33}$$Mn$$_{0.33}$$Co$$_{0.33}$$O$$_{2}$$,Li$$_{2}$$MnO$$_{3}$$の順に結構構造が変化するのに対して、放電過程では、Li$$_{2}$$MnO$$_{3}$$,LiNi$$_{0.33}$$Mn$$_{0.33}$$Co$$_{0.33}$$O$$_{2}$$の順に結晶構造が変化することが分かった。

論文

Neutron scattering study of yttrium iron garnet

社本 真一; 伊藤 孝; 大西 弘明; 山内 宏樹; 稲村 泰弘; 松浦 直人*; 赤津 光洋*; 樹神 克明; 中尾 朗子*; 茂吉 武人*; et al.

Physical Review B, 97(5), p.054429_1 - 054429_9, 2018/02

https://doi.org/10.1103/PhysRevB.97.054429
 被引用回数：21 パーセンタイル：65.26(Materials Science, Multidisciplinary)

イットリウム鉄ガーネットの核および磁気構造と全マグノン分散を中性子散乱により調べた。低エネルギーの分散は強磁性マグノンで期待されるように14meVまで2次関数の分散を示した。$$q$$積分した動的磁化率$$chi$$"($$E$$)の虚部は低エネルギーで平方根のエネルギー依存性を示した。$$chi$$"($$E$$)から絶対値でマグノン状態密度を求めた。その値は理論的に予想されるマグノン分散でひとつのカラリティーモードに対応する。

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