Photoelectron Spectroscopy of U Oxide at LLNL
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Photoelectron Spectroscopy of U Oxide at LLNL JG Tobin1,*, S-W Yu1, BW Chung1 and GD Waddill2 1. Lawrence Livermore National Laboratory, Livermore, CA, USA 2. Missouri University of Science and Technology, Rolla, MP, USA KEYWORDS: Uranium, oxide, photoelectron spectroscopy *Corresponding Author: [email protected] Abstract X-ray photoelectron spectroscopy has been used to characterize a sample of UO2 grown on an underlying substrate of Uranium. Both AlKα (1487 eV) and MgKα (1254 eV) emission were utilized as the excitation. I Introduction In our laboratory at LLNL, an effort is underway to investigate the underlying complexity of 5f electronic structure with spin-resolved photoelectron spectroscopy using chiral photonic excitation, i.e. Fano Spectroscopy. Our previous Fano measurements with Ce indicate the efficacy of this approach [1,2] and theoretical calculations and spectral simulations suggest that Fano Spectroscopy may resolve the controversy concerning Pu electronic structure and electron correlation. [3,4] To this end, we have constructed and commissioned a new Fano Spectrometer, [5] testing it with the relativistic 5d system Pt. [6,7] Here, our preliminary photoelectron spectra of the UO2 system are presented. Much is known about uranium dioxide, as can be found in Wikipedia. [8] “Uranium dioxide or uranium(IV) oxide (UO2), also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. UO2 is used mainly as nuclear fuel, specifically as UO2 or as a mixture of UO2 and PuO2 (plutonium dioxide) called a mixed oxide (MOX fuel) for fuel rods in nuclear reactors. All uranium oxides were used to color glass and ceramics. Uranium oxide-based ceramics become green or black when fired in a reducing atmosphere and yellow to orange when fired with oxygen. Orange-colored Fiestaware is a well-known example of a product with a uranium-based glaze. Uranium oxide has also been used in formulations of enamel, uranium glass, and porcelain. Prior to 1960, uranium oxides were used as colored glazes.” [8] Photoelectron spectroscopy is a photon in-electron out process, with a simple relation governing the energetics: KE = hv – BF- φ. [9] Here, KE is the kinetic energy of the ejected electron. hv is the energy of the incoming photon. BF is the binding energy of the electron with respect to the Fermi Level (EF). φ is a work-function. In our case, φ is a spectrometerwork-function (φSP) and KE is relative to that value. For our spectrometer, φSP = 4 eV, so the relations for AlKα and MgKα excitation are as follows: KE(AlKα) = 1483 eV - BF and KE (MgKα) = 1250 - BF.
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Experimental The experiments were carried out onsite at Lawrence Livermore National Laboratory, using a spectrometer [5] with capabilities for performing both spin resolved Fano spectroscopy [6,7] and high energy Inverse Photoelectron Spectroscopy (IPES) or Bremstrahlung Isochromat Spectroscopy (BIS). [10] The PES spectra were collected using a Specs x-ray source
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