核破砕中性子源水銀標的容器の材料劣化評価に対する押込み試験技術の適用

涌井 隆; 斎藤 滋; 二川 正敏

実験力学, 24(4), p.212 - 218, 2024/12

J-PARCの核破砕中性子源水銀ターゲット容器の寿命を決定する主要な要因の一つは照射損傷である。使用済み容器の材料劣化を把握するため、使用済み容器の構造材料に対する押込み試験と数値実験による逆解析を用いた評価を行う予定である。照射量の異なる2種類のイオン照射材料に対して、この評価手法を適用した。照射量の増加に伴い、引張強度が増加し、全伸びが減少することが確認された。これらの傾向は、ばらつきを考慮した微小試験片の引張試験によって報告されている材料劣化挙動と同等である。さらに、容器は繰り返し熱負荷を受け、定格最大ビーム出力では容器の温度が140Cを超えると推定されるため、温度上昇に伴う全伸びと照射材料の疲労強度の低下について検討した。

Atom-vacancy-defect-derived electric hysteresis loops and stochastic low-frequency noises in few-atom layer MoS

小杉 美央子*; 吉川 貴史; 齊藤 英治; 他10名*

ACS Applied Materials & Interfaces, 16(46), p.64190 - 64196, 2024/11

https://doi.org/10.1021/acsami.4c13147

Atom-vacancy-defects present in various materials yield numerous interesting physical phenomena, even obstructing high performance in some cases. On the other hand, their valuable applications to novel devices, such as nitrogen vacancy centers in diamond for quantum bits, have gathered significant attention. In particular, these tendencies become more substantial in two-dimensional (2D) (atomically) thin van der Waals layers. However, correlations with various kinds of atom defects are still under exploration. Herein, we find the stochastic behaviors of large hysteresis loops with strong photoresponse in the static electrical properties in few-atom layer semiconductors, molybdenum disulfide (MoS). The temperature dependence and transmission electron microscopy reveal that they arise from pairs of two neighboring in-plane S-vacancy defects, which predominantly present only around the interface at the MoS flake/substrate, with activation energies similar to 0.35 eV. The low-frequency () (LF) noise measurements clarify a high f shift in the two 1/ 2-dependent regimes, implying stochastic behaviors of electric charges through the S-vacancy pairs with high-speed charge(spin) transitions across low kinetic energy barriers between narrow discrete states. The shallow energy sates are formed from the highly uniform S-vacancy pairs interacting with Mo atoms, which act like quantum dots. The observed stochastic operation holds promise for various application, particularly for probabilistic neuromorphic computation in artificial intelligence.

Development of a non-destructive carbon quantification method in iron by negative muon lifetime measurement

二宮 和彦*; 久保 謙哉*; 稲垣 誠*; 吉田 剛*; 竹下 聡史*; 反保 元伸*; 下村 浩一郎*; 河村 成肇*; Strasser, P.*; 三宅 康博*; et al.

Journal of Radioanalytical and Nuclear Chemistry, 333(7), p.3445 - 3450, 2024/07

https://doi.org/10.1007/s10967-023-09289-2

A novel nondestructive light element analysis method for bulk materials using muon beams was demonstrated. This method is based on the lifetime measurement of muons in a material and performed by measuring muon-decay electrons and identifying elements using the atomic number based on muon lifetimes. Muon irradiation on pure iron and two steel samples with known carbon contents was conducted to prepare a calibration curve for the quantitative analysis. We also performed a muon lifetime measurement for a Japanese sword and successfully determined its carbon content as 0.51 wt% using the calibration curve, without sample destruction.

Coexistence of quantum-spin-hall and quantum-hall-topological-insulating states in graphene/hBN on SrTiO substrate

小幡 玲二*; 齊藤 英治; 吉川 貴史; 他7名*

Advanced Materials, 36(19), p.2311339_1 - 2311339_8, 2024/05

https://doi.org/10.1002/adma.202311339

SrTiO (STO) substrate, a perovskite oxide material known for its high dielectric constant (epsilon), facilitates the observation of various (high-temperature) quantum phenomena. A quantum Hall topological insulating (QHTI) state, comprising two copies of QH states with antiparallel two ferromagnetic edge-spin overlap protected by the U(1) axial rotation symmetry of spin polarization, has recently been achieved in low magnetic field (B) even as high as approximate to 100 K in a monolayer graphene/thin hexagonal boron nitride (hBN) spacer placed on an STO substrate, thanks to the high epsilon of STO. Despite the use of the heavy STO substrate, however, proximity-induced quantum spin Hall (QSH) states in 2D TI phases, featuring a topologically protected helical edge spin phase within time-reversal-symmetry, is not confirmed. Here, with the use of a monolayer hBN spacer, it is revealed the coexistence of QSH (at B = 0T) and QHTI (at B not equal 0) states in the same single graphene sample placed on an STO, with a crossover regime between the two at low B. It is also classified that the different symmetries of the two nontrivial helical edge spin phases in the two states lead to different interaction with electron-puddle quantum dots, caused by a local surface pocket of the STO, in the crossover regime, resulting in a spin dephasing only for the QHTI state. The results obtained using STO substrates open the doors to investigations of novel QH spin states with different symmetries and their correlations with quantum phenomena. This exploration holds value for potential applications in spintronic devices.

Local structural changes in V-Ti-Cr alloy hydrides with hydrogen absorption/desorption cycling

池田 一貴*; 佐次田 頌*; 大友 季哉*; 大下 英敏*; 本田 孝志*; 羽合 孝文*; 齋藤 開*; 伊藤 晋一*; 横尾 哲也*; 榊 浩司*; et al.

International Journal of Hydrogen Energy, 51(Part A), p.79 - 87, 2024/01

https://doi.org/10.1016/j.ijhydene.2023.10.318

Low-vanadium-concentration alloys have low durability, and their hydrogen absorption and desorption amounts decrease by 20% after 100 cycles. In this study, we conducted reverse Monte Carlo modeling on X-ray diffraction patterns and neutron pair distribution functions of the hydrogen-absorbed and desorbed samples of a VTiCr alloy to analyze the variations in the local structure. The local structure surrounding the hydrogen atom in the hydrogen-absorbed phase exhibited minimal changes. In contrast, hydrogen occupied both tetrahedral and octahedral sites of the hydrogen-desorbed phase almost equally during the early cycles; however, the amount of hydrogen occupying the tetrahedral sites increased with the number of cycles.

Ga K-edge XANES study of Ga-exchanged zeolites at high temperatures under different atmospheres including vacuum, CO, and pressurized H

Huang, M.*; 金城 哲弥*; 安村 駿作*; 鳥屋尾 隆*; 松村 大樹; 齋藤 寛之*; 清水 研一*; 並木 則和*; 前野 禅*

Catalysis Science & Technology, 13(23), p.6832 - 6838, 2023/12

https://doi.org/10.1039/D3CY01250F

Ga-exchanged zeolites are promising catalysts for dehydrogenative alkane transformations. Reduced Ga species, such as Ga hydrides and Ga cations, are possible active sites for alkane dehydrogenation based on in situ spectroscopic studies. However, most of the reported studies were conducted at lower temperatures compared with those encountered in actual operating conditions. In this study, the in situ Ga K-edge XANES analysis of Ga-exchanged MFI zeolite was performed under actual operating temperatures and different atmospheres (H, He, CO, vacuum, and CH). The absorption edge appeared at similarly lower energy values than that of GaO in all atmospheres, whereas the main absorption peak intensity differed depending on the presence or absence of a hydride source in the gas phase. Higher intensities were observed under H and CH atmospheres than under CO and vacuum atmospheres.

First observation of O

近藤 洋介*; Achouri, N. L.*; Al Falou, H.*; Atar, L.*; Aumann, T.*; 馬場 秀忠*; Boretzky, K.*; Caesar, C.*; Calvet, D.*; Chae, H.*; et al.

Nature, 620(7976), p.965 - 970, 2023/08

https://doi.org/10.1038/s41586-023-06352-6

非常に中性子が過剰な原子核Oは、陽子、中性子ともに魔法数であることから古くからその性質に興味が持たれていたが、酸素の最後の束縛核Oよりも中性子が4個も多いため、これまで観測されてこなかった。この論文では、理化学研究所RIBFにてFからの1陽子ノックアウト反応によってOを生成し、そこから放出される中性子を測定することによって初めてその観測に成功した。核構造の観点からは、Oでは二重閉殻が保たれているか興味が持たれていたが、実験で得られた分光学的因子が殻模型計算で予言されて程度の大きいことから、閉殻構造をもたない可能性が高いことがわかった。

HTTR1次ヘリウム循環機フィルタの差圧上昇事象,1; 差圧上昇事象の原因調査

根本 隆弘; 荒川 了紀; 川上 悟; 長住 達; 横山 佳祐; 渡部 雅; 大西 貴士; 川本 大樹; 古澤 孝之; 猪井 宏幸; et al.

JAEA-Technology 2023-005, 33 Pages, 2023/05

JAEA-Technology-2023-005.pdf:5.25MB

HTTR (High Temperature engineering Test Reactor) RS-14サイクルの原子炉出力降下において、ヘリウムガス循環機のフィルタ差圧が上昇傾向となった。この原因を調査するため、1次ヘリウム純化設備のガス循環機の分解点検等を実施した結果、ガス循環機内のシリコンオイルミストがチャコールフィルタの性能低下で捕集できなくなり、1次系統に混入したためと推定された。今後は、フィルタ交換を実施するとともに、さらなる調査を進め、再発防止対策を策定する予定である。

Spin and spin current; From fundamentals to recent progress

前川 禎通; 吉川 貴史*; 中堂 博之; 家田 淳一; 齊藤 英治

Journal of Applied Physics, 133(2), p.020902_1 - 020902_24, 2023/01

https://doi.org/10.1063/5.0133335

Along with the progress of spin science and spintronics research, the flow of electron spins, i.e., spin current, has attracted interest. New phenomena and electronic states were explained in succession using the concept of spin current. Moreover, as many of the conventionally known spintronics phenomena became well organized based on spin current, it has rapidly been recognized as an essential concept in a wide range of condensed matter physics. In this article, we focus on recent developments in the physics of spin, spin current, and their related phenomena, where the conversion between spin angular momentum and different forms of angular momentum plays an essential role. Starting with an introduction to spin current, we first discuss the recent progress in spintronic phenomena driven by spin-exchange coupling: spin pumping, topological Hall torque, and emergent inductor. We, then, extend our discussion to the interaction/interconversion of spins with heat, lattice vibrations, and charge current and address recent progress and perspectives on the spin Seebeck and Peltier effects. Next, we review the interaction between mechanical motion and electron/nuclear spins and argue the difference between the Barnett field and rotational Doppler effect. We show that the Barnett effect reveals the angular momentum compensation temperature, at which the net angular momentum is quenched in ferrimagnets.

Nonlinear magnon polaritons

Lee, O.*; 山本 慧; 埋田 真樹; Zollitsch, C. W.*; Elyasi, M.*; 吉川 貴史*; 齊藤 英治; Bauer, G. E. W.*; 紅林 秀和*

Physical Review Letters, 130(4), p.046703_1 - 046703_6, 2023/01

https://doi.org/10.1103/PhysRevLett.130.046703

We experimentally and theoretically demonstrate that nonlinear spin-wave interactions suppress the hybrid magnon-photon quasiparticle or "magnon polariton" in microwave spectra of an yttrium iron garnet film detected by an on-chip split-ring resonator. We observe a strong coupling between the Kittel and microwave cavity modes in terms of an avoided crossing as a function of magnetic fields at low microwave input powers, but a complete closing of the gap at high powers. The experimental results are well explained by a theoretical model including the three-magnon decay of the Kittel magnon into spin waves. The gap closure originates from the saturation of the ferromagnetic resonance above the Suhl instability threshold by a coherent back reaction from the spin waves.