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Recently, it was demonstrated that an empirical model based on bremsstrahlung isochromat spectroscopy of elemental thorium (Th) could be used to explain the experimental results and unoccupied 5f electronic structure for simple localized actinide systems with n = ⅔, 2, 3, and 5, where n is the 5f occupancy. Here, the thorium model will be extended to provide an understanding of the observed behavior and unoccupied 5f electronic structure in the uranium monochalcogenide systems of uranium sulfide and uranium telluride, in terms of weak 5f delocalization. [ABSTRACT FROM AUTHOR]

Using a simple empirical model based upon the bremsstrahlung isochromat spectroscopy of elemental Th, it is possible to explain the recent high energy resolution fluorescence detection measurements of UF4 (n = 2) and UCd11 (n = 3) as well as the new inverse photoelectron spectroscopy of Pu2O3 (n = 5), where n is the 5f occupation number. A critical issue in this analysis is the assumption that the Th 5f states are essentially empty, which will be confirmed both experimentally and computationally. Thus, for 5f systems, this simple model provides a unified and consistent picture of 5f unoccupied density of states in simple, localized systems, as the 5f occupation varies in the early part of the series, for n = 0, 2, 3, and 5. [ABSTRACT FROM AUTHOR]

Delocalization in the 5f states of the actinides is an important phenomenon, but poorly quantified. Here, the fundamental limitations of 5f dispersion measurements using angle and momentum resolved variants of photoelectron spectroscopy will be discussed. A novel approach will be suggested, based on a theoretical projection, which should circumvent these limitations: M4,5 X-ray emission spectroscopy. This analysis will utilize the case study of U metal, which can be considered to be the paramount example of 5f dispersion. [ABSTRACT FROM AUTHOR]

By using M4,5 X-ray Emission Spectroscopy (XES) in the tender X-ray regime, it is possible to quantify 5f delocalization in the actinides. Previous analyses, utilizing the Branching Ratio (BR) in the N4,5 X-ray Absorption Spectroscopy (XAS), could not discriminate between the cases of localized n = 2 and delocalized n = 3, in uranium materials, where n is the number of 5f electrons on the U entity. Here, it is shown that, by employing the ubiquitous 6p → 3d XES as a point of normalization, the localized n = 2 and delocalized n = 3 cases can be easily distinguished and quantified. [ABSTRACT FROM AUTHOR]

We present a high energy resolution x-ray spectrometer for the tender x-ray regime (1.6–5.0 keV) that was designed and operated at Stanford Synchrotron Radiation Lightsource. The instrument is developed on a Rowland geometry (500 mm of radius) using cylindrically bent Johansson analyzers and a position sensitive detector. By placing the sample inside the Rowland circle, the spectrometer operates in an energy-dispersive mode with a subnatural line-width energy resolution (∼0.32 eV at 2400 eV), even when an extended incident x-ray beam is used across a wide range of diffraction angles (∼30° to 65°). The spectrometer is enclosed in a vacuum chamber, and a sample chamber with independent ambient conditions is introduced to enable a versatile and fast-access sample environment (e.g., solid/gas/liquid samples, in situ cells, and radioactive materials). The design, capabilities, and performance are presented and discussed. [ABSTRACT FROM AUTHOR]

1, there is substantial agreement between the Th model and the spectra for UO SB 2 sb ([3]) and U SB 3 sb O SB 8 sb ([4]). The U SB 3 sb O SB 8 sb spectrum of Le Pape I et al i .[4] is almost identical to that published earlier by Kvashnina and co-workers.[5] However, there is no agreement between the U(VI) uranyl cases[[4], [6]] and the Th model. The HERFD of U SB 4 sb O SB 9 sb of Kvashnina I et al i .[5] also has more than one peak, thus rendering agreement with the Th model impossible without additional information. [Extracted from the article]

Scanning micro-XRF analyses were applied in situ at the National Museum of Damascus in Syria for an analytical study of three unique gilded bronze figurines. The figurines are dated back to the Late Bronze Age (1400–1300 BC) and were discovered at the Ugarit archaeological site in Syria. The present work focuses on analytical methodologies exploiting the merits of scanning micro-XRF analyses to provide an integrated non-destructive characterization of constituent materials (gilded layer, bronze alloy) or naturally formed corrosion layers. In the case of the XRF analysis of ancient binary Cu–Sn alloys, a universal dependence of the Sn Kα to Lα characteristic lines intensity ratio is proposed as a function of the Sn concentration. This consists a simple analytical quantitative criterion to assess the suitability of the surface preservation state before proceeding with any XRF quantification analysis. The results of the present study demonstrate and highlight the potential of scanning micro-XRF to expand the analytical information obtained beyond the spatially resolved elemental composition, thus offering more insight into metallurgical techniques applied by the ancient craftsmen. [ABSTRACT FROM AUTHOR]

We present a multicrystal Johann-type hard x-ray spectrometer (∼5-18 keV) recently developed, installed, and operated at the Stanford Synchrotron Radiation Lightsource. The instrument is set at the wiggler beamline 6-2 equipped with two liquid nitrogen cooled monochromators - Si(111) and Si(311) - as well as collimating and focusing optics. The spectrometer consists of seven spherically bent crystal analyzers placed on intersecting vertical Rowland circles of 1 m of diameter. The spectrometer is scanned vertically capturing an extended backscattering Bragg angular range (88°-74°) while maintaining all crystals on the Rowland circle trace. The instrument operates in atmospheric pressure by means of a helium bag and when all the seven crystals are used (100 mm of projected diameter each), has a solid angle of about 0.45% of 4π sr. The typical resolving power is in the order of EΔE∼10 000. The spectrometer's high detection efficiency combined with the beamline 6-2 characteristics permits routine studies of x-ray emission, high energy resolution fluorescence detected x-ray absorption and resonant inelastic x-ray scattering of very diluted samples as well as implementation of demanding in situ environments. [ABSTRACT FROM AUTHOR]

We present the analytical features and performance of an x-ray spectroscopy end station of moderate energy resolution operating with proton-induced quasi-monochromatic x-ray beams. The apparatus was designed, installed and operated at the 5.5 MV Tandem VdG Accelerator Laboratory of the Institute of Nuclear Physics, N.C.S.R. 'Demokritos,' Athens. The setup includes a two-level ultrahigh vacuum chamber that hosts in the lower level up to six primary targets in a rotatable holder; there, the irradiation of pure element materials-used as primary targets-with few-MeV high current (∼μA) proton beams produces intense quasi-monochromatic x-ray beams of selectable energy. In the chamber's upper level, a six-position rotatable sample holder hosts the targets considered for x-ray spectroscopy studies. The proton-induced x-ray beam, after proper collimation, is guided to the sample position whereas various filters can be also inserted along the beam's path to eliminate the backscattered protons or/and to absorb selectively components of the x-ray beam. The apparatus incorporates an ultrathin window Si(Li) spectrometer (FWHM 136 eV at 5.89 keV) coupled with low-noise electronics capable of efficiently detecting photons down to carbon Kα. Exemplary soft x-ray spectroscopy studies and results of selective x-ray fluorescence analysis are presented. [ABSTRACT FROM AUTHOR]

We have reconstructed three-dimensional (3D) element-specific distributions of aerosol microparticles captured in a thick quartz filter. The characteristic x rays were induced by a proton microprobe and detected by a Si(Li) spectrometer equipped with a polycapillary lens. Combining a fine microbeam scanning in the lateral plane with the sample movement parallel to the beam axis, the aerosol particles were driven across the sensitive microvolume and for Fe, Ca, S, and Si a sequence of two-dimensional lateral x-ray images was recorded. This is the first example of an x-ray element selective 3D imaging of a few micrometer sized objects with a proton beam. [ABSTRACT FROM AUTHOR]

We present a new x-ray Raman spectroscopy end-station recently developed, installed, and operated at the Stanford Synchrotron Radiation Lightsource. The end-station is located at wiggler beamline 6-2 equipped with two monochromators-Si(111) and Si(311) as well as collimating and focusing optics. It consists of two multi-crystal Johann type spectrometers arranged on intersecting Rowland circles of 1 m diameter. The first one, positioned at the forward scattering angles (low-q), consists of 40 spherically bent and diced Si(110) crystals with 100 mm diameters providing about 1.9% of 4π sr solid angle of detection. When operated in the (440) order in combination with the Si (311) monochromator, an overall energy resolution of 270 meV is obtained at 6462.20 eV. The second spectrometer, consisting of 14 spherically bent Si(110) crystal analyzers (not diced), is positioned at the backward scattering angles (high-q) enabling the study of non-dipole transitions. The solid angle of this spectrometer is about 0.9% of 4π sr, with a combined energy resolution of 600 meV using the Si (311) monochromator. These features exceed the specifications of currently existing relevant instrumentation, opening new opportunities for the routine application of this photon-in/photon-out hard x-ray technique to emerging research in multidisciplinary scientific fields, such as energy-related sciences, material sciences, physical chemistry, etc. [ABSTRACT FROM AUTHOR]

Highlights: [•] A method is presented that allows fits to the whole RXES plane. [•] 5f-Orbital occupancy and delocalization are quantified using the RXES technique. [•] Samples include α-Pu, γ-Pu, PuCoGa5, PuCoIn5, and PuSb2, as well as PuO2.06. [•] FEFF calculations support delocalization estimates. [Copyright &y& Elsevier]

Abstract: A new confocal PIXE set-up at the Jožef Stefan Institute in Ljubljana was recently designed and built. It consists of a silicon-drift detector, a specially designed polycapillary lens and a snout-alignment interface for precise positioning. It allows detector movement in all directions and therefore precise alignment during the creation of the probing volume and the possibility of simultaneous use of other complementary techniques, including standard μ-PIXE measurements with another X-ray detector. A description of the new set-up is given, as well as a short presentation of the method itself. Two custom-designed types of X-ray lenses were tailored and manufactured for this application, a standard semi-lens and a polycapillary conic collimator; both were characterized and compared within the scope of development of the confocal PIXE system. First results of depth profiling with the beam scanning mode are shown. [Copyright &y& Elsevier]

Abstract: In the present work, new, differential cross-section values are presented for the natK(p, p 0) reaction in the energy range E lab =3000–5000keV (with an energy step of 25keV) and for detector angles between 140° and 170° (with an angular step of 10°). A qualitative discussion of the observed cross-section variations through the influence of strong, closely spaced resonances in the p+ 39K system is also presented. Information has also been extracted concerning the 39K(p,α 0) reaction for E lab =4000–5000keV in the same angular range. As a result, more than ∼500 data points will soon be available to the scientific community through IBANDL (Ion Beam Analysis Nuclear Data Library –http://www-nds.iaea.org/ibandl/) and could thus be incorporated in widely used IBA algorithms (e.g. SIMNRA, WINDF, etc.) for potassium depth profiling at relatively high proton beam energies. [Copyright &y& Elsevier]

Recent developments in Resonant Inelastic X-Ray Scattering Experiments have vastly improved the resolution in X-ray Spectroscopies such as X-ray Absorption. However, the use of Tender X-rays (∼3 keV) and the reactivity of actinides such as uranium have given rise to new questions about bulk and surface sensitivity, what constitutes a surface and how to characterize the formation of an oxide. It will be shown that the in situ electron scattering features that are part of the RIXS spectrum can be used to quantify the uranium oxide formation and determine cleanliness, independently of the near edge features that provide information about the unoccupied electronic density of states. [ABSTRACT FROM AUTHOR]

Resonant x-ray emission spectroscopy (RXES) was employed at the U LIII absorption edge and the Lα1 emission line to explore the 5ƒ occupancy, nƒ, and the degree of 5ƒ-orbital delocalization in the hidden-order compound URu2Si2. By comparing to suitable reference materials such as UF4, UCd11, and α-U, we conclude that the 5ƒ orbital in URu2Si2 is at least partially delocalized with nƒ=2.87±0.08, and does not change with temperature down to 10 K within the estimated error. These results place further constraints on theoretical explanations of the hidden order, especially those requiring a localized ƒ² ground state. [ABSTRACT FROM AUTHOR]

Using x-ray emission spectroscopy and absorption spectroscopy, it has been possible to directly access the states in the unoccupied conduction bands that are involved with 5f and 6d covalency in oxidized uranium. By varying the oxidizing agent, the degree of 5f covalency can be manipulated and monitored, clearly and irrevocably establishing the importance of 5f covalency in the electronic structure of the key nuclear fuel, uranium dioxide. [ABSTRACT FROM AUTHOR]

An extensive investigation of oxidation in uranium has been pursued. This includes the utilization of soft x-ray absorption spectroscopy, hard x-ray absorption near-edge structure, resonant (hard) x-ray emission spectroscopy, cluster calculations, and a branching ratio analysis founded on atomic theory. The samples utilized were uranium dioxide (UO2), uranium trioxide (UO3), and uranium tetrafluoride (UF4). A discussion of the role of nonspherical perturbations, i.e., crystal or ligand field effects, will be presented. [ABSTRACT FROM AUTHOR]