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長住 達; 長谷川 俊成; 飯垣 和彦; 中川 繁昭; 久保 真治; 島崎 洋祐; 中嶋 國弘; 櫻井 洋亮; 篠原 正憲; 齋藤 賢司; et al.
Nuclear Engineering and Design, 446, p.114542_1 - 114542_14, 2026/01
高温工学試験研究炉(HTTR)を用いて、高温ガス炉の優れた安全性を実証するため、ブロック型高温ガス炉として世界で初めて強制冷却喪失試験(LOFC試験)を実施した。本試験では、全てのヘリウムガス循環機(HGC)を停止させるとともに、制御棒の挿入を防止することで、炉心の強制冷却機能および停止機能を意図的に喪失させた。HGC停止後、炉心温度の上昇に伴って生じた負の反応度フィードバック効果により、原子炉出力は100%(30 MW)からほぼ0%まで自発的に低下した。その後、炉心温度の低下およびキセノン(Xe)の減衰により再臨界に至ったが、原子炉出力は約1.2%という低い値で安定した。さらに、本試験中および試験直後のHTTR運転中に、一次冷却材中の放射性物質濃度はほぼ変化せず、本試験に伴う炉心温度上昇後も被覆粒子燃料に破損等が生じなかったことを示した。これにより、冷却材の喪失時に制御棒を挿入しなくても原子炉は自然に止まり、冷え、放射性物質が閉じ込められるという、高温ガス炉の優れた安全性を実証した。
高木 慎弥*; 有友 嘉浩*; 中島 滉太*; 岡田 和記; 廣瀬 健太郎; 西尾 勝久
Physical Review C, 112(1), p.014608_1 - 014608_7, 2025/07
被引用回数：0 パーセンタイル：0.00(Physics, Nuclear)Kinetic energy of individual fission fragment for actinide nuclei is, for example, important for evaluating the prompt-neutron spectrum in the laboratory system. It is experimentally known that kinetic energy for each fragment is constant at about 100 MeV for light fragments and that for heavy fragments decreases linearly with mass number. Most of the theoretical studies carried out so far attempted to calculate the total kinetic energy of both fragments, i.e. sum of the energies of two fragments, but the kinetic energy of each fragment was not analyzed in detail as far as we recognize. We have calculated them in thermal-neutron induced fission of 
Pu with a dynamical model using Langevin equations within a three-dimensional two-center parametrization. Also fission of 
Fm was investigated. It is calculated from the Coulomb energy at the scission point and the pre-scission kinetic energy. It is found that the pre-scission kinetic energy has about 2-4% contribution in the kinetic energy. The calculated results reproduce the trend of the experimental data.
with geometrically frustrated orthogonal antiferromagnetic dimer目時 直人; 山内 宏樹; 萩原 雅人; 綿貫 竜太*; 河村 聖子; 古府 麻衣子*; 中島 健次; 松田 雅昌*
Physical Review B, 111(10), p.104424_1 - 104424_9, 2025/03
被引用回数：1 パーセンタイル：62.18(Materials Science, Multidisciplinary)フラストレートしたシャストリ・サザランド格子を有するNdBの磁気転移を理解する目的で中性子非弾性散乱実験を行った。
と
による準四重項状態が磁気秩序相で4つに分裂する。スペクトルは磁気相互作用
、磁気
と四極子
の結合、そして一軸的な結晶場により説明される。この
電子状態により、主たる秩序変数である面内磁気モーメント
と結く誘起された2次的な秩序変数
を説明することができた。幾何学的フラストレーションによってハイゼンベルグ相互作用が打ち消し合う状況で、磁気と四極子の結合が本質的な役割をすることが明らかになった。
MnSiO
川又 雅広*; Pang, X.*; 村川 寛*; 河村 聖子; 中島 健次; 増田 英敏*; 藤田 全基*; 花咲 徳亮*; 小野瀬 佳文*; 南部 雄亮*
Physical Review Materials (Internet), 9(1), p.014407_1 - 014407_6, 2025/01
被引用回数：1 パーセンタイル：58.55(Materials Science, Multidisciplinary)Magnetic excitations in the noncentrosymmetric magnet SrMnSiO were investigated through inelastic neutron scattering measurements. Major magnetic excitations are limited up to the energy transfer of 0.5 meV, and two magnon branches under zero magnetic field were well explained in the framework of linear spinwave theory. The magnitudes of the square-lattice in-plane and interplane nearest-neighbor interactions, spin anisotropy term, and the Dzyaloshinskii-Moriya interaction are, respectively, estimated to be J
= 45.54(5) 
eV, J = 0.52(1) eV, = 4.98(11) eV, D
= 0.02(9) eV, and D
= 4.10(1) eV, and calculations using these parameters reproduce experimental data quite well. SrMnSiO appears to have the smallest energy scale among the melilite-type compounds, and the small J/J = 0.0114(2) indicates the strong two dimensionality.
C and 500C高木 穂乃香*; 薮塚 武史*; 林田 洋寿*; Song, F.; 甲斐 哲也; 篠原 武尚; 栗田 圭輔; 飯倉 寛; 山本 典央*; 中島 稔*; et al.
Solid State Ionics, 417, p.116716_1 - 116716_7, 2024/12
被引用回数：3 パーセンタイル：41.43(Chemistry, Physical)Tracer diffusion coefficients of lithium-ions in the sintered samples of Li
Al
Ge(PO)
(LAGP) have been measured through the neutron radiography (NR) technique in the wide temperature range from 25C to 500C. The diffusion data above and below 300C were collected using pulsed and reactor-generated neutrons, respectively, which coincide with each other at 300C exhibiting a single curve in the Arrhenius plot. The room-temperature diffusion coefficient and the activation energy below 300C are obtained as 1.47
10
cm
s
and 0.37 eV, respectively. The activation energy of the conductivity diffusion coefficient almost agrees with the tracer one, and the deduced Haven ratio of 0.40 is consistent with the concerted migration model of the lithium-ions.
楡井 真実; 古府 麻衣子; 中島 健次; 菊地 龍弥*; 河村 聖子; 村井 直樹; 原田 正英; 稲村 泰弘
Journal of Neutron Research, 26(2-3), p.75 - 82, 2024/09
We investigated neutron flux at a sample position and energy resolution of a direct-geometry disk-chopper spectrometer AMATERAS under various chopper conditions and compared them with simulations and calculations. The measured flux was comparable to other similar spectrometers with high flux. The resolution when using a pulse-shaping chopper was in close agreement with the analytical calculations, including the thickness of the disk chopper, the sample size, and the penetration depth into the detector. It is found that the chopper, placed at the intermediate distance of the primary spectrometer, works as a pulse shaper that optimizes the flux and resolution below the incident energy of 10 meV.
Zhu, L.*; He, H.*; Naeem, M.*; Sun, X.*; Qi, J.*; Liu, P.*; Harjo, S.; 中島 健次; Li, B.*; Wang, X.-L.*
Physical Review Letters, 133(12), p.126701_1 - 126701_6, 2024/09
被引用回数：4 パーセンタイル：69.02(Physics, Multidisciplinary)It has long been suspected that magnetism could play a vital role in the phase stability of multi- component high-entropy alloys. However, the nature of the magnetic order, if any, has remained elusive. Here, by using elastic and inelastic neutron scattering, we demonstrate evidence of antiferromagnetic order below 
80 K and strong spin fluctuations persisting to room temperature in a single-phase face-centered cubic (fcc) CrMnFeCoNi high-entropy alloy. Despite the chemical complexity, the magnetic structure in CrMnFeCoNi can be described as 
-Mn-like, with the magnetic moments confined in alternating (001) planes and pointing toward the 
111
direction. Combined with first-principles calculation results, it is shown that the antiferromagnetic order and spin fluctuations help stabilized the fcc phase in CrMnFeCoNi high-entropy alloy.
Zeng, Z.*; Zhou, C.*; Zhou, H.*; Han, L.*; Chi, R.*; Li, K.*; 古府 麻衣子; 中島 健次; Wei, Y.*; Zhang, W.*; et al.
Nature Physics, 20(7), p.1097 - 1102, 2024/07
被引用回数：20 パーセンタイル：96.75(Physics, Multidisciplinary)Emergent quasiparticles with a Dirac dispersion in condensed matter systems can be described by the Dirac equation for relativistic electrons, in analogy with Dirac particles in high-energy physics. For example, electrons with a Dirac dispersion have been intensively studied in electronic systems such as graphene and topological insulators. However, charge is not a prerequisite for Dirac fermions, and the emergence of Dirac fermions without a charge degree of freedom has been theoretically predicted to be realized in Dirac quantum spin liquids. These quasiparticles carry a spin of 1/2 but are charge-neutral and so are called spinons. Here we show that the spin excitations of a kagome antiferromagnet, YCu(OD)
Br
[Br
(OD)
], are conical with a spin continuum inside, which is consistent with the convolution of two Dirac spinons. The predictions of a Dirac spin liquid model with a spinon velocity obtained from spectral measurements are in agreement with the low-temperature specific heat of the sample. Our results, thus, provide spectral evidence for a Dirac quantum spin liquid state emerging in this kagome lattice antiferromagnet. However, the locations of the conical spin excitations differ from those calculated by the nearest-neighbor Heisenberg model, suggesting the Dirac spinons have an unexpected origin.
-MgAgSbLi, J.*; Li, X.*; Zhang, Y.*; Zhu, J.*; Zhao, E.*; 古府 麻衣子; 中島 健次; Avdeev, M.*; Liu, P.-F.*; Sui, J.*; et al.
Applied Physics Reviews (Internet), 11(1), p.011406_1 - 011406_8, 2024/03
被引用回数：13 パーセンタイル：91.20(Physics, Applied)The desire for intrinsically low lattice thermal conductivity (
) in thermoelectrics motivates numerous efforts on understanding the microscopic mechanisms of heat transport in solids. Here, based on theoretical calculations, we demonstrate that -MgAgSb hosts low-energy localized phonon bands and avoided crossing of the rattler modes, which coincides with the inelastic neutron scattering result. Using the two-channel lattice dynamical approach, we find, besides the conventional contribution (70% at 300 K) from particlelike phonons propagating, the coherence contribution dominated by the wavelike tunneling of phonons accounts for 30% of total at 300 K. By considering dual contributions, our calculated room-temperature of 0.64 WmK well agrees with the experimental value of 0.63 WmK. More importantly, our computations give a nonstandard 
dependence, perfectly explaining the abnormal temperature-trend of 
in experiment for -MgAgSb. By molecular dynamics simulation, we reveal that the structure simultaneously has soft crystalline sublattices with the metavalent bonding and fluctuating liquid-like sublattices with thermally induced large amplitude vibrations. These diverse forms of chemical bonding arouse mixed part-crystal part-liquid state, scatter strongly heat-carrying phonons, and finally produce extremely low . The fundamental research from this study will accelerate the design of ultralow- materials for energy-conversion applications.
Li, N.*; Sun, Y.*; 中島 邦久; 黒崎 健*
Journal of Nuclear Science and Technology, 61(3), p.343 - 353, 2024/03
被引用回数：1 パーセンタイル：17.48(Nuclear Science & Technology)福島原子力発電所(1F)事故では、表面積の大きなステンレス鋼(SS304)製の気水分離器や蒸気乾燥器にセシウムが大量に残っている可能性がある。そして、1F廃止措置においてこのようなCsは、放射性粉塵を生成する可能性があるため、安全上問題になることが予想される。しかし、水酸化セシウム(CsOH)の化学吸着により生成した酸化被膜の付着強度については、まだ、明らかになっていない。本研究では、CsOHによる化学吸着がどの程度酸化被膜の付着強度に影響するかスクラッチ試験機を用いて調査した。その結果、CsOHの化学吸着により酸化被膜の付着強度は低下したが、剥離させることはできなかった。
菊地 龍弥*; 川北 至信; 中島 健次; 河村 聖子; 稲村 泰弘
Journal of Molecular Liquids, 385, p.121868_1 - 121868_10, 2023/09
We investigated the diffusion dynamics of liquid benzene as a basic molecular liquid. Quasielastic neutron scattering (QENS) was utilized to elucidate the overall behavior of molecular diffusion in liquid benzene. Mode distribution analysis, which does not require specific model assumptions and can describe molecular dynamics by QENS as a distribution of Lorentz functions, revealed that the diffusion of benzene molecules is represented by three dynamic modes. The Q-dependencies of the scattering intensity and the relaxation time were analyzed using diffusion models constructed to match each dynamic mode. (1) The slowest mode is translational diffusion, described as continuous diffusion rather than jump diffusion. (2) The intermediate-speed mode is rotational diffusion, which is due to the three-dimensional reorientation of benzene molecules with a jump angle of approximately 90. (3) The fastest mode involves local fluctuations, which may originate from translational oscillations and librations of the benzene crystal. The overall picture of the diffusion dynamics and characteristics of the individual modes were clarified without using a model, which is a new approach in the field of diffusion dynamics of molecular liquids.
SnSe
Ren, Q.*; Gupta, M. K.*; Jin, M.*; Ding, J.*; Wu, J.*; Chen, Z.*; Lin, S.*; Fabelo, O.*; Rodriguez-Velamazan, J. A.*; 古府 麻衣子; et al.
Nature Materials, 22(8), p.999 - 1006, 2023/08
被引用回数：91 パーセンタイル：99.21(Chemistry, Physical)Ultralow thermal conductivity and fast ionic diffusion endow superionic materials with excellent performance both as thermoelectric converters and as solid-state electrolytes. Yet the correlation and interdependence between these two features remain unclear owing to a limited understanding of their complex atomic dynamics. Here we investigate ionic diffusion and lattice dynamics in argyrodite AgSnSe using synchrotron X-ray and neutron scattering techniques along with machine-learned molecular dynamics. We identify a critical interplay of the vibrational dynamics of mobile Ag and a host framework that controls the overdamping of low-energy Ag-dominated phonons into a quasi-elastic response, enabling superionicity. Concomitantly, the persistence of long-wavelength transverse acoustic phonons across the superionic transition challenges a proposed 'liquid-like thermal conduction' picture. Rather, a striking thermal broadening of low-energy phonons, starting even below 50 K, reveals extreme phonon anharmonicity and weak bonding as underlying features of the potential energy surface responsible for the ultralow thermal conductivity (
0.5 WmK) and fast diffusion. Our results provide fundamental insights into the complex atomic dynamics in superionic materials for energy conversion and storage.
橋本 俊輔*; 山口 聡*; 原田 雅史*; 中島 健次; 菊地 龍弥*; 大石 一城*
Journal of Colloid and Interface Science, 638, p.475 - 486, 2023/05
被引用回数：11 パーセンタイル：61.91(Chemistry, Physical)最近、粒子分率から計算される理論的に予測された値と比較して、ベース液体と分散された固体ナノ粒子で構成されるナノ流体の熱伝導率の異常な改善が報告されている。一般に、気体と液体の熱伝導率の値は、並進運動中の分子の平均自由行程によって支配される。ここでは、ナノ粒子の周りの液体分子の振動挙動がこれらの熱伝導率の増加に寄与している可能性を示す確かな証拠を提示する。
Wu, P.*; 村井 直樹; Li, T.*; 梶本 亮一; 中村 充孝; 古府 麻衣子; 中島 健次; Xia, K.*; Peng, K.*; Zhang, Y.*; et al.
New Journal of Physics (Internet), 25(1), p.013032_1 - 013032_11, 2023/01
被引用回数：1 パーセンタイル：31.85(Physics, Multidisciplinary)The understanding of the lattice dynamics is essential for engineering the thermal transport properties in quantum materials. Based on the canonical point of view, acoustic phonons are believed to be the principal thermal carriers in heat flow. Here, in this work, optical phonons are elucidated to play a pivotal role in determining the lattice thermal conductivity in thermoelectric material SnS by using the state-of-the-art inelastic neutron scattering technique combined with first-principles calculations. Additionally, in contrast to acoustic phonons, optical phonons are observed to exhibit pronounced softening and broadening with temperature. Our observations not only shed light on the significance of the optical phonons in thermal transport but also provide a vital clue to suppress the propagation of optical phonons to optimize the thermoelectric performance of SnS.
Rh
Sn
岩佐 和晃*; Suyama, Kazuya*; 河村 聖子; 中島 健次; Raymond, S.*; Steffens, P.*; Yamada, Akira*; 松田 達磨*; 青木 勇二*; 川崎 郁斗; et al.
Physical Review Materials (Internet), 7(1), p.014201_1 - 014201_11, 2023/01
被引用回数：5 パーセンタイル：44.41(Materials Science, Multidisciplinary)The spin dynamics, crystalline-electric-field (CEF) level scheme, specific heat, and X-ray photoemission spectra (XPS) of CeRhSn were investigated, which exhibits anomalous semimetal transport in the chiral crystallographic phase. CEF excitations observed at approximately 7 and 39 meV are consistent with the two inequivalent Ce-ion cites in the chiral structure. Because of broader CEF excitations and a strong 4
peak at the Fermi level in the Ce 4 on-resonance spectrum, the hybridized Ce 4 electrons contribute to the semimetal carriers. In addition, the spin fluctuation associated with the Kramers doublet ground state is characterized by the peak located at 0.15 meV. The electronic state involving the spin fluctuation causes the 
behavior of specific heat below 0.6 K, which is attributed to linear dispersion relations of electrons of the Weyl Kondo semimetal in the chiral-lattice symmetry.
中島 健次; 菊地 龍弥*; 河村 聖子; 神原 理*
EPJ Web of Conferences, 272, p.02012_1 - 02012_8, 2022/11
パルス源の冷中性子チョッパー分光計であるAMATEASで、単一測定条件での時間枠を増やす試みのいくつかを紹介する。方法の1つは、飛行時間図で介在する軌道を許可することにより、
で選択可能な使用可能な幅を増やすことができるということである。われわれの経験に基づいて、パルス源でのチョッパー分光計でのパルス繰り返し周波数増倍に基づく多色測定の条件について説明する。広帯域多色測定の最適化と一般化された定式化された条件が提案される。既存の分光計および最適化されたチョッパー分光計の基準設計へのわれわれのアイデアの適用についても説明し、パルス整形チョッパーを変更することによって効率を改善するさらなる可能性を示唆する。
石川 諒椰*; 鈴木 正敏*; 木野 康志*; 遠藤 暁*; 中島 裕夫*; 岡 壽崇; 高橋 温*; 清水 良央*; 鈴木 敏彦*; 篠田 壽*; et al.
KEK Proceedings 2022-2, p.61 - 66, 2022/11
福島県の野生ニホンザルの肝臓・膀胱・大腿筋を用いて、低線量放射線による生物影響の要因と考えられる酸化ストレスとその防御機構である抗酸化活性のバランスを調べた。その結果、福島第一原子力発電所事故に起因する非常に低い線量率の放射線被ばくによって、事故から7年から10年が経過しても放射線に対する生物の応答反応が外部被ばく・内部被ばくに共通して持続すること、その変動傾向は臓器によって異なるものの、いずれも酸化ストレスと抗酸化機構が関連して変動する可能性が示唆された。
左近 敦士*; 橋本 憲吾*; 佐野 忠史*; 中嶋 國弘*; 神田 峻*; 後藤 正樹*; 深谷 裕司; 沖田 将一朗; 藤本 望*; 高橋 佳之*
KURNS Progress Report 2021, P. 100, 2022/07
高温ガス炉の核特性を取得するための炉雑音解析技術の開発を京都大学臨界集合体(KUCA)を用い行っている。最新研究では、燃料集合体から55cm離れた検出器によりパワースペクトル密度の測定が行われた。しかしながら、即発中性子減衰定数は他の検出器から得られるものからの差異が発生した。そこで、本研究では炉外検出器によるパワースペクトル法による炉雑音解析を目的とする。
深谷 裕司; 沖田 将一朗; 神田 峻*; 後藤 正樹*; 中嶋 國弘*; 左近 敦士*; 佐野 忠史*; 橋本 憲吾*; 高橋 佳之*; 宇根崎 博信*
KURNS Progress Report 2021, P. 101, 2022/07
日本原子力研究開発機構では、2018年から高温ガス炉の核的予測技術向上に係る研究開発を開始した。その目的は、商用炉初号基のためのフルスケールモックアップ実験を回避するために一般化バイアス因子法を導入することと黒鉛減速特性を生かした中性子計装システムの改良である。このために、B7/4"G2/8"p8EU(3)+3/8"p38EU炉心をKUCAのB架台に2021年に構築した。
-dependent collective relaxation dynamics of glass-forming liquid Ca
K
(NO)
investigated by wide-angle neutron spin-echoLuo, P.*; Zhai, Y.*; Falus, P.*; Garc
a Sakai, V.*; Hartl, M.*; 古府 麻衣子; 中島 健次; Faraone, A.*; Z, Y.*
Nature Communications (Internet), 13, p.2092_1 - 2092_9, 2022/04
被引用回数：13 パーセンタイル：75.82(Multidisciplinary Sciences)The relaxation behavior of glass formers exhibits spatial heterogeneity and dramatically changes upon cooling towards the glass transition. However, the underlying mechanisms of the dynamics at different microscopic length scales are not fully understood. We measured the -dependent coherent intermediate scattering function of a prototypical ionic glass former CaK(NO), in the highly viscous liquid state. In contrast to the structure modulated dynamics for 2.4 
, i.e., at and below the structure factor main peak, for 
2.4 , beyond the first minimum above the structure factor main peak, the stretching exponent exhibits no temperature dependence and concomitantly the relaxation time shows smaller deviations from Arrhenius behavior. This finding indicates a change in the dominant relaxation mechanisms around a characteristic length of 2.6 AA, below which the relaxation process exhibits a temperature independent distribution and more Arrhenius-like behavior.
