メスバウアー分光と核共鳴非弾性散乱による鉄カルコゲン化合物の研究

京都大学0048新制・課程博士博士(理学)甲第18067号理博第3945号新制||理||1568(附属図書館)30925京都大学大学院理学研究科物理学・宇宙物理学専攻(主査)教授 瀬戸 誠, 教授 鶴 剛, 教授 大久保 嘉高学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDGA

Slow Processes in Supercooled o-Terphenyl: Relaxation and Decoupling

過冷却液体中のミクロなスケールでの固体的振る舞いの観測に成功 -液体状態の基礎理解とガラス転移の解明に期待-. 京都大学プレスリリース. 2012-09-15.We mapped the relaxation times of inter- and intramolecular correlations in o-terphenyl by a quasielastic scattering method using nuclear resonant scattering of synchrotron radiation. From the obtained map, we found that the slow β process is decoupled from the α process at 278 K, and this temperature is clearly below the previous decoupling temperature of 290 K, at which the α-relaxation dynamics changes. Then, it was also concluded that sufficient solidlike condition achieved by further cooling from 290 K is required to decouple the slow β process from the α process and, due to the difference of the length scales between the α and the slow β processes, these two averaged relaxation times are concluded not to cross as an extrapolation assumed so far. Furthermore, evidence of the restricted dynamics of the slow β process could be obtained as an anomalous momentum transfer (q) dependence of ( ∝ q-2.9) at 265 K, observed at q values of 18–48 nm-1

Pure Nuclear Bragg Reflection due to Combined Magnetic and Quadrupole Interaction in Fe3O4

A pure nuclear Bragg reflection due to the combined magnetic and quadrupole interaction in the B-site Fe of Fe3O4 hasbeen investigated. The 10 10 0 reflection (Bragg angle B = 46.48º), which is electrically allowed for the A-site Fe but forbidden for the B-site Fe, was used to measure the reflection spectra. The measurements were conducted by 57Fe synchrotron Mössbauer diffractometer at SPring-8 BL11XU using a natural iron Fe3O4 single crystal. We have succeeded, for the first time, in observing the B-site emission spectrum due to the pure nuclear Bragg reflection in case an external magnetic field of 0.08 T is applied parallel to [ 11] direction. On the other hand, in case an external magnetic field is applied parallel to [001] direction, ratio of the B-site spectrum clearly decreases as a result of partial alignmentof the magnetic moment in the [001] direction. Coexistence of the A- and B-site spectra results in the interference effect, such as broadening of the lines, asymmetric line shapes, and a slope of the base line.The analysis can be well conducted byusing the Fano function. We found that the pure nuclear Bragg reflection gives sharper line shapes than the usual nuclear resonant scattering. We also show a possible application of the pure nuclear Bragg reflection to measure the crystal site selective spectra of Fe3O4 for a future study

Development of (125)Te synchrotron-radiation-based Mössbauer spectroscopy

Proceedings of the 32nd International Conference on the Applications of the Mössbauer Effect (ICAME 2013) held in Opatija, Croatia, 1–6 September 2013The Mössbauer spectra of the 35.49 keV excited state of 125Te were observed in the energy domain using synchrotron radiation for the first time. The obtained isomer shifts and Debye temperature agree with previous experiments. These results show that this method will be applicable to various compounds

Synchrotron Mössbauer Di ff raction of Natural Iron Fe3BO6

We have succeeded in obtaining the crystal-site-selective spectra of thenatural iron Fe 3 BO 6 by using a high-sensitive 57Fe synchrotron Mössbauerdiffractometer at SPring-8 BL11XU. In the spectra measured by using thepure nuclear Bragg reflections, most of the dynamical effects of γ-raydiffraction disappear, but the higher-order interference effect between theclose nuclear energy levels still survives

Crystal-Site-Selective Spectrum of Fe3BO6by Synchrotron Mössbauer Diffraction with Pure Nuclear Bragg Scattering

We have succeeded in obtaining the crystal-site-selective spectra of the collinear antiferromagnet Fe3BO6 using a synchrotron Mössbauer diffractometer with pure nuclear Bragg scattering at SPring-8 BL11XU. Well-resolved 300, 500, and 700 reflection spectra, having asymmetric line shapes owing to the higher-order interference effect between the nuclear energy levels, were quantitatively analyzed using a formula based on the dynamical theory of diffraction. Reasonable hyperfine parameters were obtained. The intensity ratio of Fe1 to Fe2 subspectra is in accordance with the nuclear structure factor. However, when the spectrum is measured at the peak position of the rocking curve (very near the Bragg position), the value of the center shift deviates from its intrinsic value. This is also due to the dynamical effect of γ-ray diffraction. To avoid this problem, it is necessary to use diffraction angles near the foot of the rocking curve, approximately 0.02° apart from the peak position

Synchrotron radiation-based Mössbauer spectra of 174Yb measured with internal conversion electrons

電子検出により放射光メスバウアー吸収分光法の測定効率を大幅向上 -さらに多くの元素について放射光メスバウアー分光測定が可能に-. 京都大学プレスリリース. 2014-02-27.A detection system for synchrotron-radiation (SR)-based Mössbauer spectroscopy was developed to enhance the nuclear resonant scattering counting rate and thus increase the available nuclides. In the system, a windowless avalanche photodiode (APD) detector was combined with a vacuum cryostat to detect the internal conversion (IC) electrons and fluorescent X-rays accompanied by nuclear de-excitation. As a feasibility study, the SR-based Mössbauer spectrum using the 76.5 keV level of 174Yb was observed without 174Yb enrichment of the samples. The counting rate was five times higher than that of our previous system, and the spectrum was obtained within 10 h. This result shows that nuclear resonance events can be more efficiently detected by counting IC electrons for nuclides with high IC coefficients. Furthermore, the windowless detection system enables us to place the sample closer to the APD elements and is advantageous for nuclear resonant inelastic scattering measurements. Therefore, this detection system can not only increase the number of nuclides accessible in SR-based Mössbauer spectroscopy but also allows the nuclear resonant inelastic scattering measurements of small single crystals or enzymes with dilute probe nuclides that are difficult to measure with the previous detection system

(61)Ni synchrotron radiation-based Mössbauer spectroscopy of nickel-based nanoparticles with hexagonal structure.

ニッケルナノ粒子の放射光メスバウアー吸収分光測定に成功 --先端ナノ材料の機能発現メカニズムの解明に期待--. 京都大学プレスリリース. 2016-02-18.We measured the synchrotron-radiation (SR)-based Mössbauer spectra of Ni-based nanoparticles with a hexagonal structure that were synthesised by chemical reduction. To obtain Mössbauer spectra of the nanoparticles without (61)Ni enrichment, we developed a measurement system for (61)Ni SR-based Mössbauer absorption spectroscopy without X-ray windows between the (61)Ni84V16 standard energy alloy and detector. The counting rate of the (61)Ni nuclear resonant scattering in the system was enhanced by the detection of internal conversion electrons and the close proximity between the energy standard and the detector. The spectrum measured at 4 K revealed the internal magnetic field of the nanoparticles was 3.4 ± 0.9 T, corresponding to a Ni atomic magnetic moment of 0.3 Bohr magneton. This differs from the value of Ni3C and the theoretically predicted value of hexagonal-close-packed (hcp)-Ni and suggested the nanoparticle possessed intermediate carbon content between hcp-Ni and Ni3C of approximately 10 atomic % of Ni. The improved (61)Ni Mössbauer absorption measurement system is also applicable to various Ni materials without (61)Ni enrichment, such as Ni hydride nanoparticles