Taikan Harami

Synchrotron radiation beamline to study radioactive materials at the Photon factory

Abstract Design and construction of a new beamline have been described. The beamline is housed in a specially designed area controlled for radioactive materials at the Photon Factory (PF) in the National Laboratory for High Energy Physics (KEK). The beamline system consists of a front-end and two branchlines. One of the branchlines is used for X-ray photoelectron spectroscopy and radiation biology in the energy range of 1.8-6 keV and the other for X-ray diffractometry and XAFS studies as well as radiation biology in the range of 4–20 keV. The former was particularly equipped for the protection against accidental scattering of radioactive materials both inside and outside of the vacuum system.

EXAFS study of Ce1-xGdxO2-x/2

Abstract The local structures around Ce and Gd atoms in Ce1−xGdxO2−x/2 (x=0–0.30) were studied by means of extended X-ray absorption fine structure (EXAFS) spectrometry. Oxygen vacancies introduced by doping trivalent Gd ion to CeO2 were seen to be located around both Gd and Ce ions. The association of two Gd ions and one oxygen vacancy is proposed in heavily doped solid solutions, supporting the decrease in the ionic conductivity in the heavily doped region previously reported.

EXAFS analyses of CaTiO3 doped with Ce, Nd and U

Abstract The EXAFS (extended X-ray absorption fine structure) analyses were carried out for Ti–K, Ce–L3, Nd–L3 and U–L3 edges to make clear the local structures in (Ca 1− x Ce x )TiO 3 ( x =0.10, 0.20), (Ca 1− x Nd x )TiO 3 ( x =0.05, 0.10, 0.15, 0.20) and (Ca 1− x U x )(Ti 1−2 x Al 2 x )O 3 ( x =0, 0.05). With increasing neodymium content in (Ca 1− x Nd x )TiO 3 the first nearest titanium–oxygen distances decreased. On the other hand, with increasing cerium content in (Ca 1− x Ce x )TiO 3 , the first nearest titanium–oxygen distances increased. The first nearest titanium–oxygen distance in (Ca 1− x U x )(Ti 1−2 x Al 2 x )O 3 was larger than that in undoped CaTiO 3 . With increasing dopant content, the first nearest dopant (cerium or neodymium)–oxygen distances increased. From the result of the compositional dependencies of bonding length (cation–oxygen distance), which is inversely proportional to the bonding energy, it is estimated that magnitude of the leaching rate of Ce-doped CaTiO 3 is larger than those of Nd-doped and undoped CaTiO 3 . The experimental results on the leaching rates of doped and undoped CaTiO 3 were consistent with this estimation. The structural change of (Ca 0.80 Ce 0.20 )TiO 3 after a leaching test in HCl at 363 K for 140 days was also measured by X-ray diffraction and XANES analysis.

Cryogenically Cooled Monochromator with Multi‐crystal Switching System on BL11XU at SPring‐8

We developed a multi‐crystal switching system on a cryogenically cooled monochromator of the JAERI materials science beamline, BL11XU at SPring‐8. In order to make progress in our science, it is necessary to ensure at least the energy range of 6 ∼ 70 keV which is achieved by employing Si(111) and Si(311) crystals. The principle of the crystal switching is that, two crystals is arranged side by side, and they are translated in the horizontal direction for exchanging the crystals. Indium sheets were inserted between the crystals in order to improve the thermal contact. Four adjustment stages of the SPring‐8 standard type monochromator were removed to avoid the crystal vibration. A sheet heater was installed on the α‐axis stage to prevent the over‐cooling of the residual adjustment stages. The cryogenically cooled monochromator provides the 7.4 times higher flux intensity at 14.4 keV in comparison with a previous indirect water‐cooling diamond (111) crystal monochromator. It takes only 5 minutes to exchange the crystal from Si(111) to Si(311) and adjust crystals geometry. This mechanism will be easily applied to other crystals, for example asymmetrical‐cut crystals or more pair of the crystals.

CONCEPTUAL DESIGN OF SPRING-8 FRONT ENDS

The conceptual design of the front ends have been completed for the SPring‐8 under construction in Japan. Standardizing the front ends and sharing the heat load among the beamline components are the philosophy for the design. Taking the beam properties into consideration, three types of the front ends which correspond to the undulator, multipole wiggler, and bending magnet beamlines are designed.

Mössbauer Time Spectra of the Nuclear Forward Scattering from Coherently Vibrating Resonant Nuclei

The time evolution of the nuclear forward scattering from an antiferromagnetic 57FeBO3 single crystal exposed to an RF magnetic field synchronized with synchrotron radiation was investigated. The resonant nuclei were coherently vibrated by the RF magnetic field in a crystal. In the measured time spectra, intensity enhancement appeared when the initial magnetization state of the crystal was restored. The measured time spectra were analyzed by applying the multiple nuclear resonant absorption theory to the system of vibrating nuclei.

Flux Growth and Characterization of α-57Fe2O3 Single Crystals for Nuclear Bragg Scattering Optical Components

57Fe-enriched hematite, α-57Fe2O3, single crystals for the X-ray optical components of nuclear Bragg scattering (NBS) have been successfully grown by the PbO-V2O5 flux method. The X-ray rocking curves for selected areas obtained by the double-crystal method reveal that the minimum value of full width at half-maximum for the rhombohedral (6 6 6)r reflection is 2.3 arcs for λ=1.12 A. Two types of imperfections, slight bending and sector zoning are observed in the crystals by precise X-ray topography and gonlometry. The maximum counting rate of NBS (14.4 eV photons) using the best crystal with (7 7 7)r reflection is as high as 20000 cps, which has been observed using the X-ray beam from the synchrotron radiation of TRISTAN, at National Laboratory for High Energy Physics (KEK), Tsukuba.

EXAFS study of SrCeO3 doped with Yb

Abstract The local structures around Sr, Ce and Yb such as the M–O and M–M (M=Sr, Ce and Yb) interatomic distances in proton conductive Sr(Ce 1− x Yb x )O 3 ( x =0–0.2) were studied by means of extended X-ray absorption fine structure (EXAFS) spectrometry. The Sr–Ce/Yb, Ce–O and Yb–O interatomic distances of Sr(Ce 1− x Yb x )O 3 are almost constant in contrast to the decrease of its lattice constant. These results suggest that the oxygen vacancies are not located preferentially around either host Ce ions or dopant Yb ions.

Application of synchrotron radiation to analysis of local structures in energy-related materials

Our recent results on the local structures around a specified atom in several kinds of energy-related materials, i.e., Mg doped UO2 as a new type of nuclear fuel, (La 1−xMx)2Zr2O7 (MNd or Ce) as a promising ceramic matrix for fixation of TRU elements, and La 2(Zr1−xYx)2O7, Ba(Ce1−xYx)O3 and Sr(Ce0.95Yb0.05)O3 as a protonic conductor, determined by EXAFS using synchrotron radiation are summarized in relation to their anticipated functional properties.

Vibrational dynamics of some amorphous and quasicrystalline alloys

Inelastic nuclear resonance scattering has been used to get partial vibrational density of states (PVDOS) of iron in two classes of systems: (i) quasicrystalline Al 63.5 Cu 24 Fe 12.5 , its rhombohedral approximant and Al 70 Cu 20 Fe 10 crystalline (tetragonal) phase and (ii) amorphous Fe 80 B 20 and its crystalline counterpart. PVDOS in quasicrystalline phase consists of a rather broad maximum at 28 meV with a small hump at 21 meV, and is somewhat similar to that in crystalline Al 70 Cu 20 Fe 10 . Results suggest some similarity in the iron environment in quasicrystalline, approximant and crystalline phases. Amorphous Fe 80 B 20 exhibits an excess density of states as compared to the crystalline phase in the energy range 4-21 meV, which may be attributed to the boson peak.