Distinguishing ion dynamics from muon diffusion in muon spin relaxation

伊藤 孝; 門野 良典*

Journal of the Physical Society of Japan, 93(4), p.044602_1 - 044602_7, 2024/04

https://doi.org/10.7566/JPSJ.93.044602

We propose a model to describe the fluctuations in the internal magnetic field due to ion dynamics observed in muon spin relaxation (SR) by an Edwards-Anderson-type autocorrelation function that separates the quasi-static and dynamic components of the correlation by the parameter (where ). Our Monte Carlo simulations for this model showed that the time evolution of muon spin polarization deviates significantly from the Kubo-Toyabe function. To further validate the model, the results of simulations were compared with the SR spectra observed in a hybrid organic-inorganic perovskite FAPbI [with FA referring to HC(NH)], where local field fluctuations associated with the rotational motion of FA molecules and quasi-static fields from the PbI lattice are presumed to coexist. The least-squares curve fitting showed reasonable agreement with the model with , and the fluctuation frequency of the dynamical component was obtained. This result opens the door to the possibility of experimentally distinguishing fluctuations due to the dynamics of ions around muons from those due to the self-diffusion of muons. On the other hand, it suggests the need to carefully consider the spin relaxation function when applying SR to the issue of ion dynamics.

Measurement of the neutron capture cross section of Re in the keV energy region

片渕 竜也*; 佐藤 八起*; 武部 花凛*; 井頭 政之*; 梅澤 征悟*; 藤岡 諒*; 齋藤 辰宏*; 岩本 信之

Journal of Nuclear Science and Technology, 6 Pages, 2024/00

https://doi.org/10.1080/00223131.2023.2298749

Measurements of the neutron capture cross section of Re have been limited in the keV energy region. In addition, existing measured data have discrepancies. In this study, the neutron time-of-flight method was employed to measure the capture cross section of Re at Tokyo Institute of Technology. The capture -rays were detected with a large volume NaI(Tl) detector. The pulse-height weighting technique was applied to obtain the capture yield. The present results were corrected for neutron scattered effects and impurities in the sample. The measured cross sections were determined with the standard capture cross section of gold in the energy range from 15 to 90 keV, and compared with measured and evaluated data. The results of the measurement provided improved accuracy relative to previous studies in the keV energy range.

Local electronic structure of interstitial hydrogen in MgH inferred from muon study

門野 良典*; 平石 雅俊*; 岡部 博孝*; 幸田 章宏*; 伊藤 孝

Journal of Physics; Condensed Matter, 35(28), p.285503_1 - 285503_13, 2023/07

https://doi.org/10.1088/1361-648X/acccc7

Magnesium hydride has great potential as a solid hydrogen (H) storage material because of its high H storage capacity of 7.6 wt%. However, its slow hydrogenation and dehydrogenation kinetics and the high temperature of 300 C required for decomposition are major obstacles to small-scale applications such as automobiles. The local electronic structure of interstitial H in MgH is an important fundamental knowledge in solving this problem, which has been studied mainly based on density functional theory (DFT). However, few experimental studies have been performed to assess the results of DFT calculations. We have therefore introduced muon (Mu) as pseudo-H into MgH and investigated the corresponding interstitial H states by analyzing their electronic and dynamical properties in detail. As a result, we observed multiple Mu states similar to those observed in wide-gap oxides, and found that their electronic states can be attributed to relaxed-excited states associated with donor/acceptor levels predicted by the recently proposed ambipolarity model. This provides an indirect support for the DFT calculations on which the model is based via the donor/acceptor levels. An important implication of the muon results for improved hydrogen kinetics is that dehydrogenation, serving as a reduction for hydrides, stabilises the interstitial H state.

2022年度夏期休暇実習報告

石塚 悦男; Ho, H. Q.; 北川 堪大*; 福田 理仁*; 伊藤 諒*; 根本 将矢*; 楠木 捷斗*; 野村 拓朗*; 長瀬 颯太*; 橋本 温希*; et al.

JAEA-Technology 2023-013, 19 Pages, 2023/06

JAEA-Technology-2023-013.pdf:1.75MB

「HTTRに関する技術開発」をテーマとした2022年度夏期休暇実習において、5つの大学から8名が参加した。参加者は、原子力電池の検討、HTTR炉心の燃焼解析、Cf製造の検討、冷却機能喪失時の挙動解析、炉容器近傍の熱流動解析について実習した。実習後のアンケートでは、就業体験として有益であったこと、一部の学生においては自身の研究に役立ったこと、他の大学生との議論が良い経験となった等の感想があり、本実習は概ね良好な評価を得た。

Present status of J-PARC MUSE

下村 浩一郎*; 幸田 章宏*; Pant, A. D.*; 名取 寛顕*; 藤森 寛*; 梅垣 いづみ*; 中村 惇平*; 反保 元伸*; 河村 成肇*; 手島 菜月*; et al.

Journal of Physics; Conference Series, 2462, p.012033_1 - 012033_5, 2023/03

https://doi.org/10.1088/1742-6596/2462/1/012033

At J-PARC MUSE, since the SR2017 conference and up to FY2022, there have been several new developments at the facility, including the completion of a new experimental area S2 at the surface muon beamline S-line and the first muon beam extraction to the H1 area in the H-line, mainly to carry out high-statistics fundamental physics experiments. Several new studies are also underway, such as applying negative muon non-destructive elemental analysis to the analysis of samples returned from the asteroid Ryugu in the D2 area of the D-line. This paper reports on the latest status of MUSE.

Difference in expansion and dehydration behaviors between NH- and K-montmorillonite

川喜田 竜平; 齋藤 彬人*; 佐久間 博*; 安楽 総太郎; 菊池 亮佑*; 大竹 翼*; 佐藤 努*

Applied Clay Science, 231, p.106722_1 - 106722_7, 2023/01

https://doi.org/10.1016/j.clay.2022.106722

Montmorillonite (Mt) expansion and swelling are key factors for barrier performance of bentonite in trans-uranic (TRU) and high-level radioactive waste disposals. In the case of co-located geological disposal of TRU waste with high level waste, ammonium ion (NH) which is changed from nitrate ion leached from TRU waste has possibility to contact with bentonite, exchange interlayer cation of Mt to form NH-Mt, and deteriorate its performance. Because of similar hydration energy of NH to K, NH-Mt could have lower expandability or change to non-expandable mineral as reported on K-Mt. Therefore, expansion and alteration behaviors of NH-Mt, especially comparison to the behaviors of K-Mt, are necessary to understand for safety assessment of the waste disposal. In this study, the hydration behavior of NH-Mt was investigated by XRD and molecular dynamics (MD) simulation in comparison with K-Mt. XRD profiles under Relative Humidity (RH) control showed that expansion of NH-Mt was similar to that of K-Mt at more than RH40% with slightly different d-values. However, expansion of NH-Mt kept at lower than RH20%, while K-Mt easily dehydrate at the same RH. MD simulation revealed that hydrogen bonding (HB) in NH molecules causes the difference in hydration behavior between NH- and K-Mt, as HB cause larger basal spacing at dehydrated state and easier hydration. This gap on hydration may attribute the difference in alteration to non-expandable minerals after dehydration, indicating that NH have lower possibility for alternation and smaller effect on barrier performance of bentonite than K.

Laser-driven neutron generation realizing single-shot resonance spectroscopy

余語 覚文*; Lan, Z.*; 有川 安信*; 安部 勇輝*; Mirfayzi, S. R.*; Wei, T.*; 森 隆人*; Golovin, D.*; 早川 岳人*; 岩田 夏弥*; et al.

Physical Review X, 13(1), p.011011_1 - 011011_12, 2023/01

https://doi.org/10.1103/PhysRevX.13.011011

Neutrons are powerful tools for investigating the structure and properties of materials used in science and technology. Recently, laser-driven neutron sources (LDNS) have attracted the attention of different communities, from science to industry, in a variety of applications, including radiography, spectroscopy, security, and medicine. However, the laser-driven ion acceleration mechanism for neutron generation and for establishing the scaling law on the neutron yield is essential to improve the feasibility of LDNS. In this paper, we report the mechanism that accelerates ions with spectra suitable for neutron generation. We show that the neutron yield increases with the fourth power of the laser intensity, resulting in the neutron generation of in at a maximum, with Wcm, 900 J, 1.5 ps lasers. By installing a "hand-size" moderator, which is specially designed for the LDNS, it is demonstrated that the efficient generation of epithermal (0.1-100 eV) neutrons enables the single-shot analysis of composite materials by neutron resonance transmission analysis (NRTA). We achieve the energy resolution of 2.3% for 5.19-eV neutrons 1.8 m downstream of the LDNS. This leads to the analysis of elements and isotopes within sub-s times and allows for high-speed nondestructive inspection.

Repeatable photoinduced insulator-to-metal transition in yttrium oxyhydride epitaxial thin films

小松 遊矢*; 清水 亮太*; 佐藤 龍平*; Wilde, M.*; 西尾 和記*; 片瀬 貴義*; 松村 大樹; 齋藤 寛之*; 宮内 雅浩*; Adelman, J. R.*; et al.

Chemistry of Materials, 34(8), p.3616 - 3623, 2022/04

https://doi.org/10.1021/acs.chemmater.1c03450

Here, we demonstrate such a highly repeatable photoinduced insulator-to-metal transition in yttrium oxyhydride (YOH) epitaxial thin films. The temperature () dependence of the electrical resistivity () of the films transforms from insulating to metallic () under ultraviolet laser illumination. The sample is heated (125 C) under an Ar atmosphere to recover its original insulating state. The films recover their original metallic conductivity when subsequently subjected to ultraviolet laser illumination, showing repeatable photoinduced insulator-to-metal transition. First principles calculations show that the itinerant carriers originate from the variations in the charge states of the hydrogen atoms that occupy octahedral interstitial sites. This study indicates that tuning the site occupancy (octahedral/tetrahedral) of the hydrogen atoms exerts a significant effect on the photoresponse of metal hydrides.

東海再処理施設周辺の環境放射線モニタリング結果; 2020年度

中田 陽; 中野 政尚; 金井 克太; 瀬谷 夏美; 西村 周作; 根本 正史; 飛田 慶司; 二川 和郎; 山田 椋平; 内山 怜; et al.

JAEA-Review 2021-062, 163 Pages, 2022/02

JAEA-Review-2021-062.pdf:2.87MB

核燃料サイクル工学研究所では、「日本原子力研究開発機構核燃料サイクル工学研究所再処理施設保安規定、第IV 編環境監視」に基づき、再処理施設周辺の環境放射線モニタリングを実施している。本報告書は、2020年4月から2021年3月までの間に実施した環境放射線モニタリングの結果、及び大気、海洋への放射性物質の放出に起因する周辺公衆の線量算出結果について、取りまとめたものである。なお、上記の環境放射線モニタリングの結果において、2011年3月に発生した東京電力株式会社(2016年4月1日付けで東京電力ホールディングス株式会社に変更)福島第一原子力発電所事故で放出された放射性物質の影響が多くの項目でみられた。また、環境監視計画の概要、測定方法の概要、測定結果及びその経時変化、気象統計結果、放射性廃棄物の放出状況、平常の変動幅の上限値を超過した値の評価について付録として収録した。

Bayesian sparse modeling of extended X-ray absorption fine structure to determine interstitial oxygen positions in yttrium oxyhydride epitaxial thin film

熊添 博之*; 五十嵐 康彦*; Iesari, F.*; 清水 亮太*; 小松 遊矢*; 一杉 太郎*; 松村 大樹; 齋藤 寛之*; 岩満 一功*; 岡島 敏浩*; et al.

AIP Advances (Internet), 11(12), p.125013_1 - 125013_5, 2021/12

https://doi.org/10.1063/5.0071166

This letter presents a Bayesian sparse modeling method to analyze extended X-ray absorption fine structure (EXAFS) data with basis functions built on two-body signals. This method allows us to evaluate regression coefficients proportional to the radial distribution functions of the respective elements and their errors and is very effective for analysis of EXAFS with weak absorption intensity and severe signal-to-noise ratio. As an application example, we used it to analyze EXAFS of an yttrium oxyhydride (YOH) epitaxial thin film. This EXAFS data shows weak absorption intensity due to the small amount of X-ray absorption in the thin film sample. However, this approach revealed that the radial distance ratio of the second neighbor yttrium to the first neighbor oxygen coincides with that of a tetrahedral configuration. This result demonstrates that the interstitial oxygen position is tetrahedral in the YOH thin film.