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It is demonstrated here that the spectral simulation program FEFF can be adapted to include the effects of 5f total angular momentum coupling in the fluorite actinide dioxide systems ThO2, UO2, and PuO2. N4,5 x-ray absorption spectra produced with this modified FEFF approach will be compared to the previous experimental results, obtaining a strong agreement between the two.

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.

This is a combined experimental and theoretical study of the compound UO2, UO2(NO3)2(H20)6 and UO0.75Pu0.25O2, using resonant inelastic x-ray scattering (RXIS), high resolution x-ray absorption (XAS) and LDA and LDA-U calculations.

Uranium and Plutonium are highly reactive elements that undergo not only chemical reactions but also nuclear reactions. This can lead to possibly significant materials degradation, a matter of potentially great concern. Here, the issue of the electronic structure changes that occur with oxidation and radiological aging will be addressed, in a fairly empirical manner. In essence, the sensitivity of various electron spectroscopic techniques to oxidation and aging will be surveyed and discussed, including the apparent limitations. It will be found that 5d and 4d X-ray absorption and electron energy loss are essentially blind to the changes corresponding to oxidation and aging in U and Pu.

Using Synchrotron-Radiation-based Photoelectron Spectroscopy and X-ray Absorption Spectroscopy, the theoretical results within recent progress reports supplied under Contract B590089 have been evaluated. Three appendices are included: A is from Progress Report I; B is from Progress Report II; and C is from an earlier calculation by M. Ryzhkov. The comparisons between the LLNL experimental data and the Russian calculations are quite favorable. The Cluster calculations may represent a new and useful avenue to address unresolved questions within the field of actinide electron structure, particularly that of Pu.

After the CMMD Seminar by Sung Woo Yu on the subject of the x-ray spectroscopy of UO2, there arose some questions concerning the XAS of UO2. These questions can be distilled down to these three issues: (1) The validity of the data; (2) The monchromator energy calibration; and (3) The validity of XAS component of the figure shown. The following will be shown: (1) The data is valid; (2) It is possible to calibrate the monchromator; and (3) The XAS component of the above picture is correct. The remainder of this document is in three sections, corresponding to these three issues.

This contract supports the enhancement of physical protection or nuclear material control and accounting systems at institutes or enterprises of the newly independent states under the material protection control and accounting (MPC&A) program. The contract is entered into pursuant to the MPC&A Program, a gratuitous technical assistance program, in accordance with the bilateral Agreements between the Russian Federation and the United States of America concerning the Safe and Secure Transportation, Storage and Destruction of Weapons and the Prevention of Weapons Proliferation of June 1992, as extended and amended by Protocol signed of June 1999, Agreement between the Government of the Russian Federation regarding Cooperation in the Area of Nuclear Materials Physical Protection, Control and Accounting of October 1999 and the Russian Federation law of May 1999 on the taxation exemption of gratuitous technical assistance with Russian Federation under registration No.DOE001000.

We are developing and utilizing photon dichroic and spin resolved techniques to investigate electron correlation in complex systems. These materials include potential spintronic device sources such as Fe/GaAs and f electronic materials such as non-magnetic {delta}-Pu. We are pursuing Double Polarization Photoelectron Dichroism measurements of the Fano Effect, using spin resolving detection in photoelectron spectroscopy, to test the nature of electron correlation in Pu. (See Pubs 2, 4 & 5.) If successful, we will solve the riddle of Pu electronic structure that has remained unresolved for the last 60 years. We are also developing a Bremstrahlung Isochromat Spectroscopy (BIS) capability to permit the direct measurement of the unoccupied electronic structure of Pu, which is another missing piece in the puzzle of Pu electronic structure.

While chemically toxic and highly radioactive, Pu may be the most scientifically interesting element in the periodic table. It's properties include the following: six different phases, close to each other in energy and sensitive to variations of temperature, pressure and chemistry; the face-centered-cubic phase (delta) is the least dense; Pu expands when it solidifies from the melt; and it is clearly the nexus of the actinide binary phase diagrams of the actinides. In a sense, it is the boundary between the light (ostensibly delocalized 5f electrons) and heavy (ostensibly localized or correlated 5f electrons) actinide elements, but this is an over-simplification. The localized atomic 5f states are naturally correlated, but important regimes of correlated electron states are conceivable as extended states on the delocalized side of the possible Mott transition between conductive and insulating behavior. The proximity to this crossover may be the driving force behind all these exotic properties. Pu remains of immense scientific and technological importance and the advancement to a firm, scientific understanding of the electronic structure of Pu and its compounds, mixtures, alloys and solutions is a crucial issue. Moreover, while there are a number of ongoing experimental efforts directed at determining the occupied (valence band,more » below the Fermi Energy) electronic structure of Pu, there is essential no experimental data on the unoccupied (conduction band, above the Fermi Energy) electronic structure of Pu. Our objective is to determine the conduction band (unoccupied) electronic structure of Pu and other actinides (and possibly rare earths as well), in a phase specific fashion and emphasizing bulk contributions. This is world-class science directed at issue that is central to LLNL and DOE: Pu structure property relationships.« less

In preparation for the upcoming Pu Workshop in Livermore, CA, USA, during July 14 and 15, 2006, we have begun to give some thought as to how the meeting will be structured and what will be discussed. Below, you will find our first proposal as to the agenda and contents of the meeting. From you, we need your feedback and suggestions concerning the desirability of each aspect of our proposal. Hopefully, we will be able to converge to a format that is acceptable to all parties. First, it now appears that we will be limited to three main sessions, Friday morning (July 14), Friday afternoon (July 14) and Saturday morning (July 15). The Pu Futures Meeting will conclude on Thursday, July 13. Following a social excursion, the Russian participants will be transported from Monterey Bay to their hotel in Livermore. We anticipate that the hotel will be the Residence Inn at 1000 Airway Blvd in Livermore. However, the hotel arrangements still need to be confirmed. We expect that many of our participants will begin their travels homeward in the afternoon of Saturday, July 15 and the morning of Sunday, July 16. Associated with the three main sessions, we propose thatmore » there be three main topics. Each session will have an individual focus. Because of the limited time available, we will need to make some judicious choices concerning the focus and the speakers for each session. We will also have a poster session associated with each session, to facilitate discussions, and a rotating set of Lab Tours, to maximize participation in the tour and minimize the disruption of the speaking schedule. Presently, we are planning a tour of the Dynamical Transmission Electron Microscope (DTEM) facilities, but this is still in a preliminary stage. We estimate that for each session and topic, there will be time for five (5) speakers. We propose that, typically, there be three (3) Russian and two (2) American speakers per session. We also propose that each session have a chair (or two chairs), who will be given a small amount of time to set the stage for the upcoming talks and pose previously prepared, crucial questions. While this imposes a significant burden upon the session chairs, it seems to us that such an arrangement will maximize the impact of each session. While some of the topics overlap with those at Pu Futures, we propose that there will be enough complementarity and amplification of specific topics that the overlap will be minimal.« less

Synchrotron-radiation-based photoelectron spectroscopy has been used to probe the electronic structure of Ni{sub 2}MnGa. In particular, the variation of the valence band at temperatures near the transformation temperature for the martensite has been followed. Two salient results have been obtained. (1) The valence electronic structure does not seem to vary in the temperature region associated with phonon softening (near room temperature). (2) Changes in the electronic structure at the lower (martensitic) transformation temperature (T{sub M}=220K) have been observed, which agree with theoretical density of states calculation. These changes are indicative of Fermi Surface Nesting.

Using magnetic ultrathin films (2–4 monolayers) of Fe on Cu(001) and bulklike Fe, the Fe 3p and Fe 3s core states have been investigated with resonant photoemission and core‐level photoemission, including magnetic x‐ray circular dichroism (MXCD) experiments. The resonant photoemission experiment has been done, to probe the parentage of various spectral structures. All the observations can be explained as simply due to the presence of Auger features: It is not necessary to invoke configuration interaction combined with strong photoemission resonance.

Angle-resolved photoemission (ARP) of valence bands is a mature technique that has achieved spectacular success in band-mapping metals, semiconductors, and insulators. The purpose of the present study was the development of experimental and analytical techniques in ARP which take advantage of third generation light sources. Here the authors studied the relatively simple Cu surface in preparation for other metals. Copper and related metals themselves are of current interest, especially due to its role as an interlayer in spin valves and other magnetic heterostructures. A major goal of this study was the development of a systematic technique to quickly (i.e. in a few hours of synchrotron beamtime) measure the FS and separate it into bulk and surface FS`s. Often, one needs to avoid bulk features altogether, which one can achieve by carefully mapping their locations in k-space. The authors will also show how they systematically map Fermi surfaces throughout large volumes of k-space, and, by processing the resulting volume data sets, provide intuitive pictures of FS`s, both bulk and surface.

The valence band maximum of semiconductor clusters shifts with size. We attribute this phenomenon to both quantum confinement and dielectric solvation effects.

We have performed an extensive angle‐resolved photoelectron spectroscopy investigation of the surface‐alloying phenomena in the system Au/Cu(001), utilizing resonance lamp emission and synchrotron radiation. The alloy surface state, near M in the Cu(001) surface Brillouin zone, and the Au 4 f core levels exhibit significant binding‐energy shifts as a function of adsorbate coverage and substrate temperature. These and other changes are indicative of the formation and subsequent elimination of the surface‐alloy structure. Our new results will allow the consolidation of a vast body of previous results, including low‐energy electron diffraction, Auger electron spectroscopy, and photoemission measurements of Au/Cu(001), bulk Cu1−x Aux alloys, Cu3 Au(001), and Au(111).