XAFS study on americium dioxide, americium sesquioxide and uranium-americium mixed oxide solid solution

Nishi, Tsuyoshi; Nakada, Masami; Suzuki, Chikashi; Shibata, Hiroki; Okamoto, Yoshihiro; Akabori, Mitsuo; Hirata, Masaru

no journal, , 

We performed XAFS studies of americium dioxide (AmO), americium sesquioxide (AmO) and uranium-americium mixed oxide (UAmO) solid solution. EXAFS results on the Am-L absorption edge of AmO and AmO were in good agreement with crystallographic data obtained from XRD analysis. In the results of XANES spectra for AmO and AmO, an energy shift of a white line peak was observed at 4 eV, which is consistent with the chemical shift between Am and Am. The XANES result on the Am-L absorption edge of UAmO solid solution was almost in agreement with that of AmO. This result suggested that Am in the uranium-americium mixed oxide was in the trivalent state.

Study on reductive sorption of selenium(IV,VI) onto pyrite using a micro X-ray absorption spectroscopy

Kitamura, Akira

no journal, , 

Selenium-79 is one of the important elements for performance assessment of geological disposal of high-level radioactive waste. Selenium is redox sensitive thus migration behavior of selenium will be complicated. Based on these circumstances, the interaction of Se(IV,VI) species with pyrite under nearly anoxic conditions was investigated using micro X-ray spectroscopy (-XAS). Polished chips of natural pyrite were reacted with 10 mol dm NaSe(IV)O or NaSe(VI)O solutions at 80 C during two months. Micro X-ray Fluorescence (-XRF) maps and -XAS spectra were collected in suitable sample holders flushed with inert gas at the Swiss Light Source, using a beam focused to roughly 1x1 m. A highly heterogeneous distribution of Se on the pyrite surface was observed on the -XRF maps. Several highly-concentrated Se spots of a few m size were detected, surrounded by areas with low and uniform Se-level distribution. Micro X-ray Absorption Near-Edge Spectra (-XANES) in both regions indicate that Se(IV) and Se(VI) were partially reduced to Se(0).

Chemical state analysis of interface between oxides and organic molecules studied by XAFS

Narita, Ayumi; Baba, Yuji; Sekiguchi, Tetsuhiro; Shimoyama, Iwao; Hirao, Norie; Yaita, Tsuyoshi

no journal, , 

It is difficult to immobilize organic molecules on an inorganic material, because the lattice constants of organic crystals are larger than those of inorganic ones. Especially, there are few reports about the immobilization of organic molecules on oxide. In this study, we have investigated that the immobilization of alkane molecules on oxide surfaces. Octadecyl-triethoxy-silane (ODTS) molecules were adsorbed on a sapphire single crystal, and the chemical states of the interfaces were measured by X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) using synchrotron radiation. The Si 1s XPS spectrum of ODTS monolayer on sapphire suggested that silicon alokoxides of ODTS formed chemical bond with the surface. For Si-K edge XAFS spectra of ODTS monolayer, the polarization dependence was observed. On the basis of the angle dependence, it was elucidated that one of the Si-O bonds in the ODTS molecule is perpendicular to the surface.

Facility of radioactive materials beamline at KEK

Hirao, Norie; Baba, Yuji; Sekiguchi, Tetsuhiro; Shimoyama, Iwao; Okamoto, Yoshihiro; Suzuki, Shinichi; Yaita, Tsuyoshi; Usami, Noriko*; Kobayashi, Katsumi*

no journal, , 

We report here the facility of radioactive materials beamline at KEK (High Energy Accelerator Research Organization). The beamline was designed and built by Japan Atomic Energy Agency (JAEA). The experimental stations of BL-27 are located inside the "hot" laboratory where radioactive materials or samples including U or Th can be handled, in order to irradiate these samples with synchrotron X-rays. The beamline is divided into two branch lines; one is BL-27A for soft X-rays (1.8 to 6 keV) and the other is BL-27B for X-rays (4 to 20 keV). In BL-27A, irradiation apparatuses for radiobiology, photoelectron spectrometer (XPS) and photoelectron emission microscopy (PEEM) are installed in tandem. In BL-27B, irradiation apparatuses for radiobiology and XAFS spectrometer are inside hatch. This beamline is equipped with XAFS experiments (transmission XAFS, fluorescent XAFS and Imaging XAFS).

Microscopic structure formed in the organic phase upon the extraction of Zr(IV)-HNO/tributylphosphine-octane; Small-angle scattering study of the third phase formation

Motokawa, Ryuhei; Suzuki, Shinichi; Yaita, Tsuyoshi

no journal, , 

no abstracts in English

Local-structure of GdZrO and GdTiO probed by EXAFS and Gd-Moessbauer methods

Okamoto, Yoshihiro; Fuentes, A.*; Takahashi, Masashi*; Takeda, Masuo*; Nakamura, Akio

no journal, , 

NMR studies in actinide dioxides

Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku

no journal, , 

We review our recent NMR studies carried out in dioxides of the uranium and transuranium elements. Neptunium dioxide was thought for many years to be an antiferromagnet; however, neither Mssbauer spectroscopy nor neutron diffraction detected any ordered moment below the transition temperature of 26 K. It is now recognized that the phase transition originates from octupole moments. The octupolar-order scenario was suggested initially by resonant X-ray scattering and then strongly supported by our O NMR studies. Recently, we have also performed an O NMR for the first time on Americium dioxide. Our results include a drastic broadening of the NMR spectrum, after a sudden drop of NMR signal intensity below the transition temperature. These data provide the first microscopic evidence for a phase transition as a bulk property in this system.