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秋葉 宙*; 大政 義典*; 古府 麻衣子*; Zhang, M.*; 佐藤 駿*; 山室 修*
Journal of the Physical Society of Japan, 93(9), p.091010_1 - 091010_6, 2024/09
被引用回数：0 パーセンタイル：0.00(Physics, Multidisciplinary)AGNES is a direct geometry chopper-type time-of-flight neutron spectrometer installed at the cold neutron guide (C3-1-1) of JRR-3 (Tokai, Japan). This instrument is well-suited for studies on low-energy excitations of powdered and amorphous samples, and quasi-elastic scattering with an energy resolution of 120 
eV (standard mode) or 50 eV (high-resolution mode). During the long shutdown period of JRR-3 due to the Great East Japan Earthquake in 2011, AGNES was significantly improved through the installation of supermirror-coated neutron guide tubes and collimator, installation of a new-type top-loading cryo-furnace, and renewal of data acquisition electronics and software. As a result, the neutron intensity has increased by 7.7 times in the standard mode and by 3.2 times in the high-resolution mode. These enhancements facilitate experiments with small amounts of samples, and under special environments, which have previously been challenging.
大政 義典*; 高木 茂幸*; 戸嶋 健人*; 横山 凱乙*; 遠藤 亘*; 折茂 慎一*; 齋藤 寛之*; 山田 武*; 川北 至信; 池田 一貴*; et al.
Physical Review Research (Internet), 4(3), p.033215_1 - 033215_9, 2022/09
Quasielastic neutron scattering (QENS) and neutron powder diffraction of the complex transition metalhydrides Li
MoH
and Li
NbH were measured in a temperature range of 10-300 K to study their structures and dynamics, especially the dynamics of the hydrogen atoms. These hydrides contain unusual ninefold H coordinated complex ions (MoH
or NbH
) and hydride ions (H
). A QENS signal appeared 
150 K due to the relaxation of H atoms. The intermediate scattering functions derived from the QENS spectra are well fitted by a stretched exponential function called the Kohlrausch-Williams-Watts functions with a small stretching exponent 
0.3-0.4, suggesting a wide relaxation time distribution. The 
dependence of the elastic incoherent structure factor is reproduced by the rotational diffusion of MH
(M = Mo or Nb) anions. The results are well supported by a van Hove analysis for the motion of H atoms obtained using first-principles molecular dynamics calculations. We conclude that the wide relaxation time distribution of the MH rotation is due to the positional disorder of the surrounding Li ions and a unique rotation with MH anion deformation (pseudorotation).
永谷 清信*; 八尾 誠*; 早川 鉄一郎*; 大政 義典*; 梶原 行夫*; 石井 真史*; 片山 芳則
Physical Review Letters, 89(24), p.243401_1 - 243401_4, 2002/12
被引用回数：16 パーセンタイル：64.72(Physics, Multidisciplinary)中性の自由クラスターのサイズ選択EXAFS(広域X線吸収微細構造)に関する新しい方法を提案した。そこでは、X線吸収過程のみならず、下方遷移過程もまた構造情報を得るために用いられる。この方法を実験的に実証するため、われわれはEXAFSと光電子光イオンコインシデンスを同時に測定する方法を開発し、第3世代強力X線源を用いることによってセレンクラスタービームに対する実験を行った。セレンの小さなクラスターに対するEXAFSスペクトルが得られ、理論的な予言と批判的に比較された。
