No abstract available

[en] Synchrotron radiation (SR) methods have been utilized with increasing frequency over the past several years to study topics in actinide science, ranging from those of a fundamental nature to those that address a specifically-targeted technical need. In particular, the emergence of microspectroscopic and fluorescence-based techniques have permitted investigations of actinide materials at sources of soft x-ray SR. Spectroscopic techniques with fluorescence-based detection are useful for actinide investigations since they are sensitive to small amounts of material and the information sampling depth may be varied. These characteristics also serve to simplify both sample preparation and safety considerations. Examples of investigations using these fluorescence techniques will be described along with their results, as well as the prospects for future investigations utilizing these methodologies

[en] Resonant soft X-ray emission spectroscopy has been demonstrated to possess interesting abilities for studies of electronic structure in various systems, such as symmetry probing, alignment and polarization dependence, sensitivity to channel interference, etc. In the present abstract the authors focus on the feasibility of resonant soft X-ray emission to probe low energy excitations by means of resonant electronic X-ray Raman scattering. Resonant X-ray emission can be regarded as an inelastic scattering process where a system in the ground state is transferred to a low excited state via a virtual core excitation. The energy closeness to a core excitation of the exciting radiation enhances the (generally) low probability for inelastic scattering at these wavelengths. Therefore soft X-ray emission spectroscopy (in resonant electronic Raman mode) can be used to study low energy d-d excitations in transition metal systems. The involvement of the intermediate core state allows one to use the selection rules of X-ray emission, and the appearance of the elastically scattered line in the spectra provides the reference to the ground state

[en] O2p- and Cu3d - state electron density distribution of a number of bismuthates and cuprates is studied by method of X ray emission spectroscopy. High energy shift of OK_α-spectrum both in the photon energy scale and in the scale relative to Fermi level observed by transition from semiconductor to conductor in the La_2-xSr_xCuO₄ and YBa₂Cu₃O_7-x systems may be explained by rearrangement O2p-states of oxygen atoms located at the tops of CuO-pyramids (octahedrons). Correlation between T_c value and energy localization of O2p-band relative to E_F in the cuprate order, superconducting transition temperature of which varies from 35 up to 125 K is determined

[en] Resonant soft x-ray Raman scattering measurements on NiO have been made at photon energies across the Ni 2p absorption edges. The details of the spectral features are identified as Raman scattering due to d-d and charge-transfer excitations. The spectra are interpreted within the single-impurity Anderson model, including multiplets, crystal-field and charge-transfer effects. At threshold excitation, the spectral features consists of triplet-triplet and triplet-singlet transitions of the 3d⁸ configuration. For excitation energies corresponding to the charge-transfer region in the Ni 2p x-ray absorption spectrum of NiO, the emission spectra are instead dominated by charge-transfer transitions to the 3d⁹ L^-1 final state. Comparisons of the final states with other spectroscopical techniques are also made. (author)

[en] Orbital-resolved O Kα x-ray fluorescence spectra of in-CuO₂-plane [O(1)] and apical [O(2)] oxygen atoms were obtained for La_1.9Sr_0.1CuO₄ by making an appropriate choice of the energy of incident photons and the crystal orientation relative to the polarization vector of the incoming radiation. The site origin of 2p_x,y and 2p_z components in the Sr-doping-induced absorption prepeak near the O 1s edge, associated with states developed in the energy gap, was studied by O Kα monitoring at the excitation energy of the prepeak. The spectral analysis, based on the O Kα shape difference between inequivalent O sites, supports the assignment of the doping-induced 2p_x,y holes to the O(1) atoms but suggests that the 2p_z holes may have both O(2) and O(1) character in contrast to assignments in prior studies. (author). Letter-to-the-editor

[en] Spectacular changes in the optical and electrical properties were recently discovered in metal-hydride films of yttrium and lanthanum near their metal-insulator transitions: the dihydrides are excellent metals and the trihydrides are insulators and transparent in the visible part of optical spectrum. Such changes are best described by a model based on negatively charged hydrogen (H^-) ions. We have studied the electronic structure of the similar Gd-H system by X-ray Absorption and Resonant Inelastic Soft X-ray Scattering (RIXS) Spectroscopies. During our measurements we found charge transfer excitations, which produce charge-transfer satellite systems. These satellites result support the view that hydrogen is an electron acceptor

[en] This study illustrates how the damage from copper corrosion can be reduced by modifying the chemistry of the copper surface environment. The surface modification of oxidized copper films induced by chemical reaction with Cl^- and HCO₃^- in aqueous solutions was monitored by in situ X-ray absorption spectroscopy. The results show that corrosion of copper can be significantly reduced by adding even a small amount of sodium bicarbonate. The studied copper films corroded quickly in chloride solutions, whereas the same solution containing 1.1 mM HCO₃^- prevented or slowed down the corrosion processes

[en] Full text: The spin transition in LaCoO₃ is investigated by temperature-dependent resonant X-ray emission spectroscopy near the Co 2p absorption edges. This element-specific technique is more bulk sensitive with respect to the temperature induced spin-state of the Co³⁺ ions in LaCoO₃ in comparison to other high-energy spectroscopic methods. The spin transition is interpreted and discussed with ab-initio density-functional theory within the fixed-spin moment method which is found to yield consistent spectral functions to the experimental data. The spectral changes for LaCoO₃ as a function of temperature suggest a change in spin-state as the temperature is raised from 85 to 300 K while the system remains in the same spin state as the temperature is further increased to 510 K

[en] The interaction of actinides with corroded iron surfaces was studied using resonant inelastic x-ray scattering (RIXS) spectroscopy at actinide 5d edges. RIXS profiles, corresponding to the f-f excitations are found to be very sensitive to the chemical states of actinides in different systems. Our results clearly indicate that U(VI) (as soluble uranyl ion) was reduced to U(IV) in the form of relatively insoluble uranium species, indicating that the iron presence significantly affects the mobility of actinides, creating reducing conditions. Also Np(V) and Pu (VI) in the ground water solution were getting reduced by the iron surface to Np(IV) and Pu (IV) respectively. Studying the reduction of actinides compounds will have an important process controlling the environmental behavior. Using RIXS we have shown that actinides, formed by radiolysis of water in the disposal canister, are likely to be reduced on the inset corrosion products and prevent release from the canister