Study on the relation between the crystal structure and thermal stability of FeUO and CrUO

Akiyama, Daisuke*; Kusaka, Ryoji; Kumagai, Yuta; Nakada, Masami; Watanabe, Masayuki; Okamoto, Yoshihiro; Nagai, Takayuki; Sato, Nobuaki*; Kirishima, Akira*

Journal of Nuclear Materials, 568, p.153847_1 - 153847_10, 2022/09

https://doi.org/10.1016/j.jnucmat.2022.153847

FeUO, CrUO, and FeCrUO are monouranates containing pentavalent U. Even though these compounds have similar crystal structures, their formation conditions and thermal stability are significantly different. To determine the factors causing the difference in thermal stability between FeUO and CrUO, their crystal structures were evaluated in detail. A Raman band was observed at 700 cm in all the samples. This Raman band was derived from the stretching vibration of the O-U-O axis band, indicating that FeCrUO was composed of a uranyl-like structure in its lattice regardless of its "x"' value. Mssbauer measurements indicated that the Fe in FeUO and FeCrUO were trivalent. Furthermore, FeCrUO lost its symmetry around Fe with increasing electron densities around Fe, as the abundance of Cr increased. These results suggested no significant structural differences between FeUO and CrUO. Thermogravimetric measurements for UO, FeUO, and CrUO showed that the temperature at which FeUO decomposed under an oxidizing condition (approximately 800 C) was significantly lower than the temperature at which the decomposition of CrUO started (approximately 1250 C). Based on these results, we concluded that the decomposition of FeUO was triggered by an ``in-crystal'' redox reaction, i.e., Fe U Fe U, which would not occur in the CrUO lattice because Cr could never be reduced under the investigated condition. Finally, the existence of Cr in FexCrUO effectively suppressed the decomposition of the FeCrUO crystal, even at a very low Cr content.

Influence of distant scatterer on air kerma measurement in the evaluation of diagnostic X-rays using Monte Carlo simulation

Tominaga, Masahide*; Nagayasu, Yukari*; Sasaki, Motoharu*; Furuta, Takuya; Hayashi, Hiroaki*; Oita, Masataka*; Nishiyama, Yuichi*; Haga, Akihiro*

Radiological Physics and Technology, 14(4), p.381 - 389, 2021/12

https://doi.org/10.1007/s12194-021-00641-3

Due to recent advance of diagnostic radiology, the increase of diagnostic radiation exposure to patient becomes problem. Diagnostic Reference Levels has been released to optimized the radiation exposure to patients in Japan recently. The evaluation of entrance surface dose (ESD) is recommended to assess the dose level for general X-ray examination. The ESD can be easily evaluated by multiplying the backscatter factor of the patient body on the free-in-air air kerma. The air kerma free-in-air value used to estimate ESD may contain X-rays scattered from obstacles located at the time of measurement, which may induce non-minor error in assessments. We therefore studied the influence of scattered X-rays on air kerma measurement under various environments (distances, field sizes, and materials). It was found that the dependence on the X-ray energy and field size was different for different materials. The X-ray contamination can be ignored for all the materials when the distance to the scatterer exceeds 35 cm.

Structure of the {U} polyoxo cluster UOCl(MeO) (x = 2.3, MeO = methoxide)

Fichter, S.*; Radoske, T.*; Ikeda, Atsushi

Acta Crystallographica Section E; Crystallographic Communications (Internet), 77(8), p.847 - 852, 2021/08

https://doi.org/10.1107/S2056989021007623

Segmental motions of proteins under non-native states evaluated using quasielastic neutron scattering

Fujiwara, Satoru*; Matsuo, Tatsuhito*; Sugimoto, Yasunobu*; Shibata, Kaoru

Journal of Physical Chemistry Letters (Internet), 10(23), p.7505 - 7509, 2019/12

https://doi.org/10.1021/acs.jpclett.9b03196

Characterization of the dynamics of disordered polypeptide chains is required to elucidate the behavior of intrinsically disordered proteins and proteins under non-native states related to the folding process. Here we develop a method using quasielastic neutron scattering, combined with small-angle X-ray scattering and dynamic light scattering, to evaluate segmental motions of proteins as well as diffusion of the entire molecules and local side-chain motions. We apply this method to RNase A under the unfolded and molten-globule (MG) states. The diffusion coefficients arising from the segmental motions are evaluated and found to be different between the unfolded and MG states. The values obtained here are consistent with those obtained using the fluorescence-based techniques. These results demonstrate not only feasibility of this method but also usefulness to characterize the behavior of proteins under various disordered states.

3D-microstructure analysis of compacted Na- and Cs-montmorillonites with nanofocus X-ray computed tomography and correlation with macroscopic transport properties

Takahashi, Hiroaki*; Tachi, Yukio

Applied Clay Science, 168, p.211 - 222, 2019/02

https://doi.org/10.1016/j.clay.2018.11.008

Microstructural and mass transport properties of compacted Na- and Cs-montmorillonites with different swelling properties were investigated by combining 3D microstructure analysis using nanofocus X-ray CT and diffusion measurement of HDO. The X-ray CT observations indicated that macropores in the dry state of compacted Na-montmorillonite are filled with gel phases, and the grain sizes of clay particles shifted toward smaller values through the saturation and swelling processes. By contrast, no gel phase and no decrease in the grain and pore volumes were observed for saturated Cs-montmorillonite. The geometrical factors of the macropores including tortuosity and geometric constrictivity of saturated Cs-montmorillonite determined by the X-ray CT was consistent with the corresponding values derived in the HDO diffusion test. In the case of Na-montmorillonite, the larger differences between the geometric factors evaluated by the X-ray CT and the diffusion tests can be explained by the electrostatic constrictivity factor and the additional geometrical factors in gel phase and interlayer that are smaller than the detection limit of the X-ray CT.

Local structure study of the iron-based systems of BaFeAs and LiFeAs by X-ray PDF and XAFS analyses

Li, S.*; Toyoda, Masayuki*; Kobayashi, Yoshiaki*; Ito, Masayuki*; Ikeuchi, Kazuhiko*; Yoneda, Yasuhiro; Otani, Akira*; Matsumura, Daiju; Asano, Shun*; Mizuki, Junichiro*; et al.

Physica C, 555, p.45 - 53, 2018/12

https://doi.org/10.1016/j.physc.2018.10.003

-dependence of local distortions in BaFeAs and LiFeAs by X-ray PDF and XAFS methods. Although PDF data exhibit anomaly at the structure transition temperature, EXAFS data exhibit no anomaly. Data supporting the local orthorhombicity at 300 K in the tetragonal phase for BaFeAs. Arguments on the origins of the 4-fold symmetry breaking in the ground average structure of the tetragonal phase.

Thermal behavior, structure, dynamic properties of aqueous glycine solutions confined in mesoporous silica MCM-41 investigated by X-ray diffraction and quasi-elastic neutron scattering

Yoshida, Koji*; Inoue, Takuya*; Torigoe, Motokatsu*; Yamada, Takeshi*; Shibata, Kaoru; Yamaguchi, Toshio*

Journal of Chemical Physics, 149(12), p.124502_1 - 124502_10, 2018/09

https://doi.org/10.1063/1.5039892

Differential scanning calorimetry, X-ray diffraction, and quasi-elastic neutron scattering (QENS) measurements of aqueous glycine solutions confined in mesoporous silica (MCM-41) were performed at different glycine concentrations, pH, and loading ratio (= mass of glycine solution / mass of dry MCM-41) in the temperature range from 305 to 180 K to discuss the confinement effect on the thermal behavior, the structure, and the dynamic properties of the solutions.

Effect of nitrogen concentration on nano-structure and high-temperature strength of 9Cr-ODS steel

Oka, Hiroshi; Tanno, Takashi; Otsuka, Satoshi; Yano, Yasuhide; Kaito, Takeji

Nuclear Materials and Energy (Internet), 16, p.230 - 237, 2018/08

https://doi.org/10.1016/j.nme.2018.05.010

Inelastic X-ray scattering of Al ( = La, Ce, = Cu, Au)

Tsutsui, Satoshi*; Kaneko, Koji; Pospisil, J.; Haga, Yoshinori

Physica B; Condensed Matter, 536, p.24 - 27, 2018/05

https://doi.org/10.1016/j.physb.2017.09.087

Experimental observation of temperature and magnetic-field evolution of the 4 states in CeFe revealed by soft X-ray magnetic circular dichroism

Saito, Yuji; Yasui, Akira*; Fuchimoto, Hiroto*; Nakatani, Yasuhiro*; Fujiwara, Hidenori*; Imada, Shin*; Narumi, Yasuo*; Kindo, Koichi*; Takahashi, Minoru*; Ebihara, Takao*; et al.

Physical Review B, 96(3), p.035151_1 - 035151_5, 2017/07

AA2017-0611.pdf:0.36MB

https://doi.org/10.1103/PhysRevB.96.035151

We revisit the delocalized character of the 4 states of CeFe in the ferromagnetically ordered phase by X-ray magnetic circular dichroism (XMCD) in X-ray absorption spectroscopy (XAS) with improved data quality using single crystals. Surprisingly, the Ce XMCD spectral shape changes significantly as a function of temperature and applied magnetic field, with no concomitant changes in the spectral shape of the Ce XAS as well as the Fe XAS and XMCD. This unusual behavior is characterized by the states in a 4 configuration mixed into the ground state. Such extreme sensitivity of the Ce 4 states to the external perturbations can be related to the magnetic instability toward an antiferromagnetic phase in CeFe. Our experimental data presented here provide valuable insights into the underlying physics in strongly-hybridized ferromagnetic Ce compounds.