Symposium Organizers
Kerri Blobaum Lawrence Livermore National Laboratory
Elaine Chandler Lawrence Berkeley National Laboratory
Ladislav Havela Charles University
M. Brian Maple University of California-San Diego
Mary Neu Los Alamos National Laboratory
OO1: Electronic Structure and Spectroscopy
Session Chairs
Ladislav Havela
M. Brian Maple
Monday PM, November 27, 2006
Hampton (Sheraton)
9:15 AM - **OO1.1
Ab initio Investigations of the Electronic Structure of Ternary Plutonium, Neptunium and Uranium Compounds.
Peter Oppeneer 1 , Saad Elgazzar 2 3 , Sebastien Lebegue 1 4 , Olle Eriksson 1 , Alexander Shick 5
1 Dept. of Physics, Uppsala University, Uppsala Sweden, 2 , IFW, Dresden Germany, 3 Dept. of Physics, Menoufia University, Shebin El-kom Egypt, 4 , CNRS-Universite Henri Poincare, Nancy France, 5 Inst. of Physics, Academy of Sciences, Prague Czech Republic
Show Abstract9:45 AM - **OO1.2
Comparative Photoemission Study of Actinide (Am, Pu, Np and U) Metals, Nitrides, and Hydrides.
Thomas Gouder 1
1 , European Commission, JRC, Institute for Transuranium Elements, Karlsruhe Germany
Show AbstractPhotoemission spectroscopy has been widely used to study the electronic structure of actinides so as to obtain a vital information on their electronic structure. The highly correlated nature of the 5f states makes this a challenging task, because of prominence of final-states effects. Their influence can be assessed from systematic studies on systems with different 5f-bandwidths. We compared pure early-actinide metals, their nitrides, and hydrides. We thus combine the inherent 5f band narrowing, due to 5f orbital contraction throughout the actinide series, with variations of chemical environment in the compounds. We observed decreasing 5f hybridization from metals to nitrides and hydrides. While for the metals, 5f localization takes places between Pu and Am, for the hydrides it occurs between UH3 and NpH3. We will present both core-level and valence band data.For the early actinides (U, Np), the 5f spectra are often discussed in terms of ground-state density of states. With approaching localization, features closely related to multiplet like structures appear. Although various simplifying models have been constructed to bridge the gap between the localized and itinerant behaviour (as the Mixed Level Model, comprising two types of f-states in energy-optimizing mixture), it seems that only more sophisticated theories yielding the spectral density (as the Dynamical Mean Field Theory) are justified for the direct comparison with photoemission spectra. On a more phenomenological level, a simple screening model assumes, that the photohole can be screened either by 5f electrons (good screening) or by 6d7s electrons (poor screening). The competition between these screening modes is the reason for the complex photoemission spectra, especially for valence band photoemission from the 5f states. In this case, final state screening of the 5fn-1 photohole-state either restores the 5fn configuration (good screening) or keeps the 5fn-1 hole state. At the localization threshold, both configurations can appear with their characteristic atomic-multiplet structures. For the 5fn configuration, which is close to the ground state, the multiplet may coexist with the band state, where the photohole is completely shielded. In this simple picture, the 5f states may therefore appear as itinerant (band state), weakly localized (5fn multiplet) or strongly localized (5fn-1 multiplet) [1]. We show that this interpretation gives a consistent view of all presented early actinide systems. Atomic multiplets account for the astonishing similarity of photoemission spectra of diverse Pu systems such as δ-Pu [2], PuSi2 [1], PuSb1-x and PuSe [3]. [1]T. Gouder, et al., Phys. Rev. B 71, 165101 (2005).[2]L. Havela, et al., Phys. Rev. B 65, 235118 (2002)[3]T. Gouder, et al., Phys. Rev. Lett. 84, 3378 (2000).
10:15 AM - OO1.3
On the Electronic Configuration in Pu: Spectroscopy and Theory.
J. Tobin 1 , Per Söderlind 1 , A. Landa 1 , K. Moore 1 , A. Schwartz 1 , J. Wills 2
1 , LLNL, Livermore, California, United States, 2 , LANL, Los Alamos, New Mexico, United States
Show Abstract10:30 AM - OO1.4
Probing the Localized/Itinerant Boundary in Pu Systems with ARPES.
J. Joyce 1 , J. Wills 2 , T. Durakiewicz 1 , K. Graham 1 , J. Sarrao 4 , E. Bauer 1 , D. Moore 3 , L. Morales 3 , O. Eriksson 5
1 Condensed Matter and Thermal Physics group, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 4 Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 5 Department of Physics, Uppsala University, Uppsala Sweden
Show Abstract10:45 AM - OO1.5
Ab initio Electronic Structure Theory of Actinide Skutterudites.
Saad Elgazzar 1 2 , Peter Oppeneer 3
1 , IFW-Dresden, Dresden Germany, 2 Dept. of Physics, Faculty of Science, Menoufia University Egypt, 3 Dept. of Physics, Uppsala University, Uppsala Sweden
Show AbstractFilled lanthanide skutterudites came in the scientific focus several years ago when a number of anomalous phenomena were discovered for this group of materials. For example, heavy-fermion superconductivity was observed for PrOs4Sb12 [1], which might be related to a novel type of pairing mechanism [2]. While lanthanide skutterudites of the composition RT4X12 (where R is a lanthanide, T a transition metal element, and X a pnictogen) have extensively been studied for several years, only recently efforts to synthesize transuranium skutterudites were undertaken. Very recently, single crystals of the new material NpFe4P12 were grown [3]. Several years ago already the skutterudite UFe4P12 was synthesized [4]. Both actinide skutterudites are interesting materials: UFe4P12 is a rare ferromagnetic insulator, in which the 5f electrons might be close to localizing in a 5f2 configuration [4]. NpFe4P12 orders also ferromagnetically below TC=23 K and it exhibits semiconducting behavior at elevated temperatures [3]. We carried out ab initio, relativistic electronic structure calculations for the actinide skutterudites, using the LSDA-DFT framework and the full-potential local orbitals (FPLO) method [5]. Our calculations reveal that much of the electronic structure of these materials can be understood within the LSDA-DFT framework, even though the localization of the 5f’s is probably underestimated in the LSDA. The calculations show that 5f states are placed around the Fermi energy, yet fall in a 1 eV wide gap of valence bands consisting mainly of Fe and P states, which is an important aspect of these materials. Since the hybridization of the 5f states with other valence states is quite small, the 5f band is quite narrow. Ferromagnetic ordering splits the 5f band such that a gap is formed for NpFe4P12; for UFe4P12 a quasi-gap is opened. The computed magnetic moment of UFe4P12 (0.67) compares reasonably well with the experimental moment of 0.5 Bohr magnetons [6]. The computed Np moment (0.49), however, is too small compared to the experimental moment of 1.33 Bohr magnetons. Our calculations indicate that actinide skutterudites are promising materials for observing localized 5f‘s, or perhaps 5f delocalized-localized transitions. A key feature is the position of the narrow 5f states in the gap, without much hybridization. This situation is similar to what has previously been found for UPd3 and UO2, which are both actinide materials with localized 5f states.[1]E.D. Bauer et al., Phys. Rev. B 65 (2002) 100506R.[2]D.E. MacLaughlin et al., Phys. Rev. Let. 89 (2002) 157001.[3]G.P. Meisner et al., J. Appl. Phys. 57 (1985) 3073.[4]D. Aoki et al., J. Phys. Soc. Jpn., in press (2006).[5]K. Koepernik and H. Eschrig, Phys. Rev. B 59 (1999) 1743.[6]H. Nakotte et al., Physica B 259 (1999) 282.
11:30 AM - **OO1.6
Electronic Structure Theory of the Ground State and Photoemission Spectra of Non-Magnetic δ-Pu, fcc-Am, and Pu-Am Alloys.
Alexander Shick 1 , Ladislav Havela 2 , Jindrich Kolorenc 1 3 , Vaclav Drchal 1
1 Condensed Matter Theory, Institute of Physics, Academy of Sciences of Czech Republic, Prague Czech Republic, 2 Faculty of Mathematics and Physics, Charles University, Prague Czech Republic, 3 Department of Physics, North Carolina State University, Raleigh, North Carolina, United States
Show Abstract12:00 PM - **OO1.7
Nature of Non-magnetic Strongly-correlated State in Plutonium.
L. Pourovskii 1 , A. Shick 2 , L. Havela 3 , M. Katsnelson 4 , Alexander Lichtenstein 5
1 , Ecole Polytechnique, Paliaseau CEDEX France, 2 , Institute of Physics ASCR, Prague Czech Republic, 3 , Charles University, Prague Czech Republic, 4 , Radbound University of Nijmegen, Nijmegen Netherlands, 5 , University of Hamburg, Hamburg Germany
Show AbstractLocal density approximation for the electronic structure calculations has been highly successful for non-correlated systems. The LDA scheme quite often failed for strongly correlated materials containing transition metals and rare-earth elements with complicated charge, spin and orbital ordering. Dynamical mean field theory in combination with the first-principle scheme (LDA+DMFT) can be a starting point to go beyond static density functional approximation and include effects of charge, spin and orbital fluctuations. Ab-initio relativistic dynamical mean-field theory is applied to resolve the long-standing controversy between theory and experiment in the "simple" face-centered cubic phase of plutonium called Δ-Pu. In agreement with experiment, neither static nor dynamical magnetic moments are predicted. In addition, the quasiparticle density of states reproduces not only the peak close to the Fermi level, which explains the large coefficient of electronic specific heat, but also main 5$f$ features observed in photoelectron spectroscopy.
12:30 PM - OO1.8
Observation of Dynamical Spin Shielding in Ce: Why It Matters for Pu Electronic Structure.
James Tobin 1 , Sung Woo Yu 1 , Takashi Komesu 2 , Brandon Chung 1 , Simon Morton 1 , G. Dan Waddill 2
1 CMS, LLNL, Livermore, California, United States, 2 Physics Dept., Univ.Missouri-Rolla, Rolla, Missouri, United States
Show AbstractUsing Fano Effect measurements [1,2] upon polycrystalline Ce, we have observed a phase reversal between the spectral structure at the Fermi Edge and the other 4f derived feature near a binding energy of 2 eV. The Fano Effect is the observation of spin polarized photoelectron emission from NONMAGNETIC materials, under chirally selective excitation, such as circularly polarized photons. Within various models, the peak at the Fermi Energy (f1 peak, quasiparticle peak, Kondo peak) is predicted to be the manifestation of the electrons which shield the otherwise unpaired spin associated with the peak at 2 eV ( f0 peak or Lower Hubbard Band). Utilizing high-energy photoelectron spectroscopy, on and off resonance, the bulk nature and f-character of both features have been confirmed. Thus, observation of phase reversal between the f0 and f1 peak is a direct experimental proof of spin shielding in Ce, confirming the original model of Gunnarsson and Shoenhammer, albeit with a slight modification.The results for Ce will discussed in light of our recent work on Pu [3-6]. The Pu results demonstrated the importance of spin-orbit splitting in the Pu 5f states, but left open the questions of electron correlation and magnetic cancellation. References 1. S.W. Yu, T. Komesu, B.W. Chung, G.D. Waddill, S.A. Morton, and J.G. Tobin, Phys. Rev. B 73, 075116 (2006) and references therein.2. J.G. Tobin, S.A. Morton, B.W. Chung, S.W. Yu and G.D. Waddill, Physica B, 378-380, xxxx (May 2006) and references therein.3. J.G. Tobin, K.T. Moore, B.W. Chung, M.A. Wall, A.J. Schwartz, G. van der Laan, and A.L. Kutepov, Phys. Rev. B 72, 085109 (2005).4. G. van der Laan, K.T. Moore, J.G. Tobin, B.W. Chung, M.A. Wall, and A.J. Schwartz, Phys. Rev. Lett. 93, 097401 (2004).5. J.G. Tobin, B.W. Chung, R. K. Schulze, J. Terry, J. D. Farr, D. K. Shuh, K. Heinzelman, E. Rotenberg, G.D. Waddill, and G. Van der Laan, Phys. Rev. B 68, 155109 (2003).6. K.T. Moore, M.A. Wall, A.J. Schwartz, B.W. Chung, D.K. Shuh, R.K. Schulze, and J.G. Tobin, “Phys. Rev. Lett. 90, 196404 (2003).AcknowledgementsThis work was performed under the auspices of the U.S. DOE, by the University of California, Lawrence Livermore National Laboratory, under contract W-7405-Eng-48.
12:45 PM - OO1.9
Electronic Structure of AC-Clusters and High-Resolution Xray Spectra of Actinides in Solids.
Nicolay Kulagin 1
1 Physics Department, Kharkov National University for Radio Electronics, Khakov Ukraine
Show AbstractThe communication is devoted to consideration of foundations and results of study of the electronic structure of original and doped ions with unfilled nf- shell in clusters and solids. Original method of study of high resolution X ray spectra which uses of fluorescence or synchrotron irradiation and ab initio SCF approach of calculation of electronic structure and properties of doped clusters and solids considered this report. It is well known that energy of X ray lines of AC and other ions depends on electronic state (valency) and environment of ions. Powerful theoretical approach for study of electronic distribution of clusters and doped crystals and calculation the valency shift of X ray lines upon change of electronic state of nl - ions in oxides, fluoride and other compounds before and after irradiation or thermal treatment was developed on bases of original SCF theory [1-2]. Relative error for energy of X Ray for ions in solids or clusters is less than 10-4 % and for energy shift error is order to 0.1 eV. For experimental study we used X Ray microanalysor as source of fluorescent irradiation and original two-crystals spectrometer tested the shape of X Ray lines with accuracy 2 - 20 meV. Minimum concentration value of doped ions which is necessary for study of the change of the electronic state of ions upon irradiation or thermal treatment is near 10-2 wt %.In the framework of the approach we studied stability and change of electronic state of the actinides and rare earths included radioactive ones and properties of separate bulk and clusters oxides such as A2O3, ABO3 and A3B2C3O12 etc. Foundations of electronic properties of doped oxides and non-stoichiometrical crystals are discussed in detail.[1] N. Kulagin, in “Physics of Laser Crystals”, eds. J.-C. Krupa, N. A. Kulagin. Kluwer Academic Publisher. Brussels. 2003. [2] N. Kulagin. Sol. Stat Chem. 178. 554 – 562 (2005)
OO2: 5f States and Superconductivity
Session Chairs
Monday PM, November 27, 2006
Hampton (Sheraton)
2:30 PM - **OO2.1
Actinide Superconductivity: PuCoGa5 and Related Materials.
Joe Thompson 1 , Nicholas Curro 1 , Tuson Park 1 , Eric Bauer 1 , John Sarrao 1
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractActinide materials play a special role in condensed matter physics, spanning behaviors of itinerant d-electron and localized 4f-electron materials. An intermediate state, found notably in Pu-based materials where 5f electrons appear to be neither fully localized nor itinerant, is particularly challenging to understand. Superconductivity in actinides enables a perspective on this problem. PuCoGa5, the first Pu-based superconductor, is superconducting at Tc=18.5 K. This relatively high Tc is unprecedented in any other actinide system but is typical of d-electron compounds in which conventional superconductivity is mediated by phonons. Recent studies of PuCoGa5 suggest, however, that its superconductivity is not conventional; rather, these experiments are consistent with superconductivity produced by antiferromagnetic fluctuations of nearly localized 5f electrons. With this perspective, a comparison of PuCoGa5 to the isostructural superconductor PuRhGa5 and the heavy-fermion analogs CeMIn5 (M=Co, Rh) leads to the conclusion that variations in an effective f-electron bandwidth are relevant for understanding their similarities and differences. A simple model of hybridization between localized f-electron and itinerant conduction-band electrons gives a plausible rationale for the correlation between Tc and a characteristic spin energy scale in these materials.
3:00 PM - **OO2.2
Systematic Investigation of The Superconducting Behavior in Aged PuCoGa5.
Frederic Jutier 1 , Eric Colineau 1 , Jean-Christophe Griveau 1 , Jean Rebizant 1 , Franck Wastin 1
1 , European Commission, Joint Research Centre, Inst. Transuranium Elements, Karlsruhe Germany
Show AbstractThe discovery of superconductivity in plutonium based systems is one of the most challenging latest phenomena observed in actinide science. On the one hand, PuCoGa5 displays superconducting behavior, with a critical temperature of Tc = 18.5 K and an upper critical field Hc2(0) estimated to exceed 70 T [1], considered to be unconventional and carried by strongly correlated 5f electrons [2]. No magnetic order has been observed down to T = 1 K but the temperature dependence of the magnetic susceptibility of PuCoGa5 is indicative of local-moment behavior close to that expected for Pu3+. Initial bulk measurements on a single crystal were reported to follow a modified Curie-Weiss behavior in the normal state with an effective moment μeff = 0.68 μB. On the other hand, the spontaneous alpha decay of Pu isotopes produces a continuous in-situ source of damages that can be related to other irradiation experiments performed on “more conventional” superconducting materials, and in this sense provides a unique field of investigations.In this work, we have undertaken to follow the evolution of the superconducting behavior as a function of damage created by self-radiation effects induced from the Pu-decay. It is shown that the critical temperature is particularly sensitive with ageing [1,3]. Hc2(0) and the critical current density Jc are at first remarkably enhanced due to the very efficient properties of the pinning centers induced by self-radiation damages, of the same order as the coherence length. Ageing effects induce also the apparition of “magnetic-like” anomalies in the electrical resistivity behavior recalling the effects observed in pure Pu-aged samples [4]. The combination of the evolution of resistivity and magnetic measurements provides some new hints of the unconventional character of the superconductivity in this class of materials.References[1] J. L. Sarrao et al., Nature 420, 297 (2002)[2] N. J. Curro et al., Nature 434, 622 (2005)[3] F. Jutier et al., Physica B 359-361, 1078 (2005)[4] M.J. Fluss et al., J. Alloys Comp. 368, 62 (2004) and references therein
3:30 PM - OO2:5f States
Break
4:30 PM - OO2.3
Tuning of Hidden Order and Superconductivity in URu2Si2 by Applied Pressure and Re Doping.
Nicholas Butch 1 2 , Jason Jeffries 1 2 , M. Maple 1 2
1 Department of Physics, University of California, San Diego, La Jolla, California, United States, 2 Institute for Pure and Applied Physical Sciences, University of California, San Diego, La Jolla, California, United States
Show Abstract4:45 PM - **OO2.4
Neutron Scattering Study on UTGa5 and NpTGa5.
Naoto Metoki 1 2
1 Advanced Science Research Center, Japan Atomic Energy Agency, Tokai Japan, 2 Dep. Physics, Tohoku University, Sendai Japan
Show Abstract5:15 PM - **OO2.5
Recent Results on Uranium.
James Smith 1 , Jason Lashley 1 , Michael Manley 1 , Bogdan Mihaila 1 , Cyril Opeil 2 , Roland Schulze 1
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Dept. of Physics, Boston College, Chestnut Hill, Massachusetts, United States
Show Abstract5:45 PM - OO2.6
Comparative Experimental Study of x-ray Absorption Spectroscopy and Electron Energy Loss Spectroscopy on Passivated U Surfaces.
Art Nelson 1 , W. Moberlychan 1 , R. Bliss 1 , W. Siekhaus 1 , T. Felter 1
1 CMS MSTD, LLNL, Livermore, California, United States
Show Abstract
Symposium Organizers
Kerri Blobaum Lawrence Livermore National Laboratory
Elaine Chandler Lawrence Berkeley National Laboratory
Ladislav Havela Charles University
M. Brian Maple University of California-San Diego
Mary Neu Los Alamos National Laboratory
OO3: Actinide Materials I
Session Chairs
Tuesday AM, November 28, 2006
Hampton (Sheraton)
9:30 AM - **OO3.1
Pinning Frequencies of the Collective Modes in $\alpha $-Uranium.
Jason Lashley 1
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show Abstract10:00 AM - **OO3.2
Lattice Dynamics of f-electron Metals from High-resolution Inelastic X-ray Scattering Measurements.
Daniel Farber 1 , Michael Krisch 2 , Alexandre Beraud 2 , Daniele Antonangeli 1
1 , Lawrence Livermore National Lab. , Livermore, California, United States, 2 , European Synchrotron Radiation Facility, Grenoble France
Show Abstract10:30 AM - OO3.3
Evolving Magnetism from Self Damage in Pu Alloys.
Scott McCall 1 , Michael Fluss 1 , Brandon Chung 1 , George Chapline 1 , Michael McElfresh 1 , Richard Haire 2
1 , LLNL, Livermore, California, United States, 2 , ORNL, Oak Ridge, Tennessee, United States
Show Abstract10:45 AM - OO3.4
Fermi surfaces and magnetic properties of PuX3.
Yoshinori Haga 1 , Dai Aoki 2 , Tatsuma Matsuda 1 , Hiroshi Yamagami 4 , Yoshiya Homma 2 , Yoshinobu Shiokawa 2 1 , Kunihisa Nakajima 3 , Yasuo Arai 3 , Yoshichika Onuki 5 1
1 Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki, Japan, 2 Institute for Materials Research, Tohoku University, Oarai, Ibaraki, Japan, 4 Department of Physics, Kyoto Sangyo University, Kyoto, Kyoto, Japan, 3 Nuclear Energy Department, Japan Atomic Energy Agency, Tokai, Ibaraki, Japan, 5 Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan
Show Abstract11:00 AM - OO3:Materials
BREAK
OO4: Actinide Materials II
Session Chairs
Tuesday PM, November 28, 2006
Hampton (Sheraton)
11:30 AM - **OO4.1
Using Correlations to Understand Changes in Actinide Bonding.
Richard Haire 1
1 , ORNL, Oak Ridge, Tennessee, United States
Show AbstractThe complexity of actinide science is well-known and an important facet for this is the changing role of the 5f electrons, which occurs not only in progressing across the series but also with different experimental parameters. The chemistries and many physical behaviors of these actinides are a reflection of their electronic natures. These are often related to and/or are dependent on interatomic distances and the particular electronic orbitals that are present. Thus, major changes are observed in going from isolated atoms in the vapor state to agglomerated atoms in the condensed state, and between the elements themselves and their compounds. Significant changes in electronic behavior have been found for these elements when they are subjected to high pressures, and establishing correlations between the behaviors of the different actinide elements across the series have been very informative. An important consideration here is the change in the interatomic distances, which alter significantly the energy of the system. The findings from high pressure studies, where interatomic distances are altered greatly, have instigated a number of theoretical calculations for understanding better what driving forces lay behind the observed changes. The calculations have improved significantly in recent times and now allow a prediction of behavior for conditions that exceed present experimental capabilities. Yet, experiment and theory still differ at times with regard to the “details” of the behaviors. With the 5f-element compounds, in contrast to the elements themselves, observed structural changes under pressure may not reflect involvement or non-involvement of their 5f electrons. This is due in part to the presence and role on non-actinide atoms in the compounds, which affect both interatomic distances as well as the type of orbitals that are available for interacting. The presentation will address the most recent findings from experimental studies and from available theoretical computations, citing both differences and agreements. This provides useful snapshots of the present insights regarding electronic changes, configurations and bonding for actinide materials. Correlations will be presented in regard to the elements’ positions in the series and the potential electronic and bonding changes that may be responsible for the behaviors observed.____________ *Research sponsored by the Division of Chemical Sciences, Geosciences and Biosciences, Office of Basic Energy Sciences, U.S. Department of Energy, under contract DE-ACO5-00OR22725 with Oak Ridge National Laboratory, managed and operated by UT-Battelle, LLC.[A contractor of the U.S. Government under contract DE-AC05-00OR22725 has authored this manuscript. The U.S. Government retains a non-exclusive, royalty-free license to publish or reproduce the published form of this document, or allow others to do so, for U.S. Government purposes]
12:00 PM - OO4.2
Specific Heat in the Pu-Am system.
Ladislav Havela 1 , Pavel Javorsky 1 , Alexander Shick 2 , Franck Wastin 3 , Eric Colineau 3
1 Department of Electronic Structures, Charles University, Faculty of Mathematics and Physics, Prague 2 Czech Republic, 2 , Institute of Physics, Academy of Sciences of the Czech Republic, Prague 8 Czech Republic, 3 , European Commission, Joint Research Centre, Institute for Transuranium Elements, Karlsruhe Germany
Show AbstractEssential information on strongly correlated systems comes from low-temperature specific heat, namely from the γ-coefficient of the electronic specific heat, which can be greatly enhanced by correlation effects over the one-electron value, given by the density of states at the Fermi level. The specific heat of δ-Pu canot be taken as well established because of problems with the δ-Pu stability and experimental hardship, but the two existing studies [1,2] indicate a relatively very high γ exceeding 50 mJ/mol K2. We undertook the study of specific heat of δ-Pu stabilized by Am, which excludes any monoclinic α' phase. In addition, the fcc lattice is somewhat expanded by the Am doping (by 3.5% for 20% Am doping). In case γ still increases due to this expansion, the high γ-value should be related to a narrow 5f band at the Fermi level. Specific heat of Pu stabilized by Am was studied in the temperature range 4.5-300 K for Am concentrations up to 20% using the Quantum Design PPMS equipment. Experimental data were corrected for effects of self heating, which were also severely restricting the lowest achieveable temperature even for the smallest samles (m < 1 mg). All Cp(T) dependencies have a qualitatively similar shape, without any anomaly which could be related to a magnetic ordering. No variations of the specific heat with magnetic field were found in the field of 9 T. The evaluation of the γ-value is difficult due to a strongly non-Debye like phonon contribution. Depending on its approximation, γ-values in the range 35-55 mJ/mol K2 can be estimated for Pu-8%Am, i.e. somewhat lower than values reported before [1,2]. Assuming that the very low γ = 2 mJ/mol K2 of Am [3] is preserved in the alloy (the Am 5f states are likely to preserve their localized character), γ/mol Pu can be evaluated as ranging between 38 and 60 mJ/mol Pu K2. With increasing Am concentration, γ appears to decrease by about 14 mJ/mol K2 for 15% Am. The results indicate that there is neither a tendency to form a magnetically ordered state due to the volume expansion, nor a tendency to a γ-increase. This excludes that the properties of δ-Pu would be dominated by a narrow 5f band at the Fermi level. A qualitative explanation why there is a lack of dramatic variations of properties in the Pu-Am system is provided by LDA+U "around mean field" calculations, correctly reproducing the lack of magnetic moments on both Pu and Am ions. [1] G.R. Stewart and R.O. Elliott, Conference Actinides 1981, Abstract booklet (Lawrence Berkeley Laboratory, Berkeley, CA, 1981) p. 206[2] J.C. Lashley et al., Phys.Rev.Letters 91 (2003) 205901 [3] J.L. Smith et al., J.Phys.(Paris) 40-C4 (1979) 138
12:15 PM - OO4.3
Atomistic Simulations of Ga Atom Ordering in Pu 5%at Ga Alloys.
Michael Baskes 1 , Shenyang Hu 1 , GuoFeng Wang 2 , Andrew Lawson 1 , Sven Rudin 1
1 MST, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Department of chemical Engineering,, Texas A&M University, College Station, Texas, United States
Show Abstract12:30 PM - OO4.4
Predicting the Mechanism of Instability in δ-Pu.
Babak Sadigh 1 , Jess Sturgeon 1
1 Chemistry and Materials Science, Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractOO5: Metallurgy
Session Chairs
Tuesday PM, November 28, 2006
Hampton (Sheraton)
2:30 PM - OO5.1
Changes in Delta-Plutonium Due to Aging as Observed by Continuous in-situ X-ray Scattering.
Cheng Saw 1 , Brandon Chung 1 , Mark Wall 1
1 MSTD-CMS, Lawrence Livermore National Laboratory, Livermore, California, United States
Show Abstract2:45 PM - OO5.2
Physical Property Changes in Plutonium Observed from Accelerated Aging using Pu-238 Enrichment.
Brandon Chung 1 , Cheng Saw 1 , Stephen Thompson 1 , Conrad Woods 1 , Bartley Ebbinghaus 1
1 , Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractThe self-irradiation of plutonium lies at the center of the age-related microstructural and physical property changes, which is an important aspect of the science-based stockpile stewardship. The self-irradiation in Pu-239 by the alpha decay process transmutes the Pu atom into uranium atom and an alpha particle, where most of the lattice damage comes from the uranium recoil. Because these self-irradiation effects would normally require decades to measure, a fraction (7.5 wt%) of more active isotope Pu-238 is added into the Pu-239 lattice to accelerated the aging process by approximately 17 times the normal rate. By monitoring the properties of the Pu-238 spiked alloy over a period of about 3.5 years, the properties of plutonium in stockpile pits can be projected for periods up to about 60 years. This paper presents the volume, density, and lattice parameters of the spiked Pu-238 alloys measured to more than 60 equivalent years in natural age. We have identified two age-related phenomena due to self-irradiation in Pu alloys that cause dimensional changes: the initial transient from the initial cascade damage and helium bubble accumulation. The third possible age-related phenomenon is void swelling, but this has not yet been observed in this study. After 60 equivalent years of aging, the accelerated alloys at 35°C have swelled in volume by 0.15 to 0.16% and now exhibit a near linear volume increase due to helium bubble in-growth. The X-ray diffraction study indicates the volume expansion during the first few years is due primarily to an increase in lattice parameter caused by Frenkel defects. This work was performed under the auspices of the U. S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48
3:00 PM - OO5.3
Kinetics of the Isothermal Martensitic Phase Transformation in Plutonium Gallium Alloys.
Benoit Oudot 1 , Kerri J.M. Blobaum 1 , Mark A. Wall 1 , Adam J. Schwartz 2
1 CMS, LLNL, Livermore, California, United States, 2 PAT, LLNL, Livermore, California, United States
Show AbstractThe isothermal martensitic delta to alpha-prime transformation in plutonium–gallium alloys is reported to have unusual double-C curve kinetics in a time-temperature-transformation (TTT) diagram. Here, we verify the double-C curve kinetics at longer times than previously reported and we suggest possible mechanisms that may result in this unusual behavior. Although the thermodynamically stable phases of a Pu-2.0 at% Ga alloy at 25°C are alpha (monoclinic) + Pu3Ga (tetragonal), the high-temperature face-centered-cubic delta phase is retained in a metastable state at ambient conditions. When the metastable delta phase is cooled to sub-ambient temperatures, a partial transformation to the monoclinic alpha-prime martensitic phase occurs. The alpha-prime phase is similar to the alpha phase, but it has Ga trapped in the lattice. The double-C curve kinetics of the delta to alpha-prime transformation were published by Orme, et al. in 1976 but have never been verified or fully explained. Here, we use differential scanning calorimetry as a novel method for acquiring TTT data. Isothermal holds between 10 and 1000 seconds confirm the existence of the double-C curve behavior. These experiments also suggest that a third-C curve may exist. Possible mechanisms for this behavior include differences in the transformation path, the transformation mechanism, the morphology of the alpha-prime products, or the nature of the alpha-prime embryos in the upper and lower C-curves.This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.
3:15 PM - OO5.4
Pressure-Induced Electronic Phase Transitions in Rare-Earth Metals.
Choong-Shik Yoo 1 , Brian Maddox 1 , Valentin Iota 1 , Jae-hyun Klepeis 1 , William Evans 1 , Hyunchae Cynn 1
1 , LLNL, Livermore, California, United States
Show Abstract3:30 PM - OO5.5
Processing and Stress Analysis of Thick Uranium Films.
Andrea Hodge 3 1 , Ron Foreman 2 , Gilbert Gallegos 2
3 Nanoscale Synthesis and Characterization Lab, LLNL, Livermore, California, United States, 1 Chemistry and Materials Science, LLNL, Livermore, California, United States, 2 Manufacturing and Materials Engineering Division, LLNL, Livermore, California, United States
Show Abstract3:45 PM - OO5.6
Uranium Hydride Formation Study as Observed by Scanning Surface Potential Imaging.
Marilyn Hawley 1 , M. Hill 1 , R. Schulze 1
1 Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show Abstract4:00 PM - OO5:Metallurgy
BREAK
OO6: Materials for Actinide Detection
Session Chairs
Tuesday PM, November 28, 2006
Hampton (Sheraton)
4:30 PM - **OO6.1
Materials for Actinide Detection: An Overview of Research Needs and Challenges.
Anthony Peurrung 1 , Gordon Graff 1 , Brian Milbrath 1
1 , Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractRecent world events have greatly heightened the need for next generation materials that support improved technology for actinide detection based upon gamma and neutron radioisotope signatures. This presentation will provide an overview with the goal of conveying both significant research accomplishments and significant ongoing challenges to the materials research community. This presentation will describe the technological approaches to actinide detection along with associated material performance needs. Both currently available and emerging materials of importance will be described. The ongoing challenges of improving the pace and effectiveness of new material discovery and development efforts will be conveyed with a particular focus on the role of science in the field of materials for actinide detection.
5:00 PM - **OO6.2
High Energy Resolution Scintillator Detectors for Radioisotope Identification.
Nerine Cherepy 1
1 Chemistry and Materials Science, Lawrence Livermore National Lab, Livermore , California, United States
Show AbstractOO7: Poster Session
Session Chairs
Wednesday AM, November 29, 2006
Exhibition Hall D (Hynes)
9:00 PM - OO7.1
Long-Term Phase and Mechanical Instability of Water-Quenched U-6Nb.
Jikou Zhou 1 , Luke Hsiung 1
1 Chemistry and Materials Science Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States
Show Abstract9:00 PM - OO7.2
Optical Properties of Plutonium Surface Oxide by Ellipsometry Between .5 and 5.5 eV Photon Energy.
Wigbeert Siekhaus 1 , Bhaskar Mookerji 1
1 Chemistry & Mat. Sciences, LLNL, Livermore, California, United States
Show Abstract9:00 PM - OO7.3
Cryogenic Nuclear Reactor Fuel and Blankets for Energy Harvesting.
Liviu Popa-Simil 1
1 , LAVM Inc., Los Alamos, New Mexico, United States
Show AbstractThe new developments in nano-structures and high-energy superconductors open the road for better nuclear energy. The development in special of Pu based superconductors is an important feature which might be used in a family of new nuclear fuels as well in energy harvesting blankets which to be used as active shielding in many nuclear application as fission, fusion and annihilation. The nano-structured superconductors may make possible the direct radiation energy harvesting by using heterogeneous structures as well creating a neutron sensitive amplification layer with usage in neutron detectors and neutron beam harvesting. The nuclear fuel is warming up, mainly by micro-looping the electrons showers generated by the fission products stopping in the fuel lattice with further transfers the energy to the phonons. These loops or electronic knock-ons displacement appears in all the fuel materials, due to the fact that the excitation energy is in the range of several KeV, which is further spread to other electrons creating a shower which mainly follows the direction of the initial highly charged fission fragment. The polarization occurred after this initial stage make the other charges in the system move and restore the equilibrium. In a nano-structure with dimensions less than the path of the electrons the polarization effects occur making possible the capability of harvesting the fission products energy directly. If the energy is directly converted in electricity driven out by super- conductive filaments the fuel will warm no more. The theoretical analysis and computer simulations shows that for optimized nano-hetero-structures conversion efficiencies greater than 80% are possible.That means that some limits of efficiency is possible of producing cryogenic nuclear reactors of ultra high efficiency. The next problem to be solved at the material level is that related to the super-conductive structures resistance to radiation damage, the self healing capability by annealing and the influence of fission products on the material properties or the development of conjugated ways to self cleaning of the nuclear material. The presence in the super-conductive material of the actinides like Pu, U, confers the superconductor the quality of nuclear fuel, being able to reach the criticality conditions needed for the nuclear reactor to operate.New aspects like the usage of quantum oscillations and Josephson effect seams beneficial to energy conversion and transport outside the reactor core become attractive research targets. In terms of potential applications there are possible the creation of new materials able to harvest and amplify the neutrons energy in fusion, annihilation applications, as well as nuclear reactor fuel assembly operating near unitary criticality like nuclear reactors or accelerator driven sub-critical assemblies.
Symposium Organizers
Kerri Blobaum Lawrence Livermore National Laboratory
Elaine Chandler Lawrence Berkeley National Laboratory
Ladislav Havela Charles University
M. Brian Maple University of California-San Diego
Mary Neu Los Alamos National Laboratory
OO8: Actinides and the Environment
Session Chairs
Wednesday AM, November 29, 2006
Hampton (Sheraton)
9:00 AM - **OO8.1
Structural Characterization of an Plutonium Sequestering Agent Complex by Synchrotron X-ray Diffraction.
Anne Gorden 1 3 , David Shuh 1 , Geza Szigethy 2 , Bryan Tiedemann 2 , Jide Xu 2 , Kenneth Raymond 1 2
1 Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Chemistry and Biochemistry, Auburn University, Auburn, Alabama, United States, 2 Chemistry, University of California, Berkeley, California, United States
Show AbstractPower generation based on nuclear fuel sources is hindered by significant waste management risks, making the optimization of process chemistry and remediation of radioactive wastes an environmental issue of tremendous importance. A resurgence of interest in actinide coordination chemistry has been inspired by a need to address these concerns, and also to expand structural diversity, to develop new separations technologies, and to further our understanding of 5f electron behavior. New ligands and materials are required that can coordinate, sense, and purify actinides for selective extraction and in decontamination applications. The similarities in the chemical, biological transport, and distribution properties of Fe(III) and Pu(IV) inspired a biomimetic approach to the development of sequestering agents for actinides based on the highly-selective hydroxypyridonate (HOPO) chelating units found in naturally occurring Fe(III) sequestering agents called siderophores. Several HOPO ligands have been developed and testsed as Pu(IV) extraction agents and as actinide decorporation agents. A detailed evaluation of the structure and bonding of actinide coordinating ligands like these is important for the design of new selective ligand systems, especially since less than 25 plutonium complexes have been characterized by single-crystal X-ray diffraction (XRD) and reported in the literature. Knowing the small size of Pu crystals resulting from these ligand systems and handling considerations, we developed procedures that utilize the Advanced Light Source (ALS) to determine the solid-state structures of Pu complexes by XRD. Using these methods, the Pu(IV)-[5LIO(Me-3,2-HOPO)]2 complex is the first in a series of plutonium-ligand complexes to be characterized. This and other similar structures will aid in the generation of a library of such complexes and provides a benchmark for future structural studies with actinides. This is the first Pu(IV) hydroxypyridonate complex to be structurally characterized, the first Pu decorporation agent complex to be characterized by single crystal XRD, and the first Pu complex characterized through the use of a single crystal small molecule XRD at a synchrotron radiation source. New projects in this area will focus on the development of ligands for selective uranium coordination for use in sensors and sensing materials, with a particular interest in systems that are less sensitive to basic conditions. Related Publications1.Gorden, A.E.V.; Xu, J.; Raymond, K. N.; Durbin, P. D. “The Rational Design of Sequestrating Agents for Plutonium and other Actinide Elements,” Chem. Rev., 2003, (11), 103, 4207 – 4282.2.Gorden, A. E. V.; Shuh, D. K.; Tiedemann, B. E. F.; Wilson, R. E.; Xu, J.; Raymond, K. N.; “Sequestered Plutonium: Pu(IV)[Bis(5-LIO-Me-3,2-HOPO)]2 – The First Structurally Characterized Plutonium Hydroxypyridonate Complex,” Chem. Eur. J., 2005, (9), 2842 - 2848.
9:30 AM - **OO8.2
Thermodynamic and Structural Characterization of Pu(IV) Coordination by Natural Siderophores Desferrioxamine B and Pyoverdin.
Sean Reilly 1 , Hakim Boukhalfa 1
1 Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show Abstract10:15 AM - OO8.4
Solution State Actinide Speciation in the Solution State as Followed by 13C and 17O NMR.
Bruce McNamara 1 , Herman Cho 1 , Lanee Snow 1 , Judah Friese 1
1 , Pacific Northwest Laboratory, Richland, Washington, United States
Show AbstractThe solution speciation of uranyl hydroxy-peroxy and uranyl peroxy-carbonato species that are formed under radiolytic conditions are not well described in the literature. It is well known that highly reactive species are produced during water radiolysis, but little work has been reported that demonstrates the physiochemical impacts of such species on actinides in spent nuclear fuel. The results discussed in this report are a continuation of studies of real time, radiation-field dependent evolution of the uranyl system under conditions relevant to storage of spent nuclear fuels. In this report, we have focused on pH regime between 6 and 9.5 and have followed by 13C, 17O NMR, UV-vis and Raman spectroscopy changes in the solution state speciation of a uranyl peroxy carbonate species that exhibit general mononuclear structures as (238U17O2(13CO3)3-x(O2)x4-) and/or multinuclear peroxo-bridged structures. These signatures are used to identify the major species produced by auto-radiolysis of weakly acidic and alkaline carbonate solutions (pH=6-9.5) using the alpha decay from the uranyl tris carbonate (233U17O2(13CO3)34-). New evidences for the coordinative mode of hydrogen peroxide to the uranyl center, kinetic data for the exchange of peroxide for carbonate and scrambling of the uranyl trans-oxo 17O-labeled oxygen in the presence of hydrogen peroxide will be discussed.
10:30 AM - **OO8.5
Actinide-Transition Metal Bonding in Gas-Phase Complexes.
John Gibson 1 , Richard Haire 1 , Joaquim Marcalo 2 , Marta Santos 2 , Antonio Pires de Matos 2
1 Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Departamento de Química, Instituto Tecnológico e Nuclear, Sacavém Portugal
Show Abstract11:00 AM - OO8:Environment
BREAK
OO9: Actinide Chemistry
Session Chairs
Wednesday PM, November 29, 2006
Hampton (Sheraton)
11:30 AM - **OO9.1
Actinide Coordination Environments in Solution and in the Solid State.
Lynda Soderholm 1 2 , S. Skanthakumar 1 , Richard Wilson 1 , Peter Burns 2 1
1 Chemistry Division, Argonne National Laboratory, Argonne , Illinois, United States, 2 Civil Engineering and Geological Sciences, University of Notre Dame, South Bend, Indiana, United States
Show Abstract12:00 PM - OO9.2
The Structures of Polynuclear Th(IV) Hydrolysis Products.
Richard Wilson 1 , S. Skanthakumar 1 , Ginger Sigmon 2 , Yung-Jin Hu 2 , Peter Burns 2 1 , L. Soderholm 1 2
1 Chemistry Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, Indiana, United States
Show Abstract12:15 PM - OO9.3
Actinides Co-conversion by Internal Gelation.
Anne-Charlotte Robisson 1 , Jacques Dauby 1 , Estelle Machon 1 , Corinne Dumont-Schintu 1 , Stéphane Grandjean 1
1 , CEA Valrhô, Bagnols sur cèze France
Show AbstractIn the frame of an optimised management of minor actinides for the future nuclear systems, the elaboration of fuels or transmutation targets from spherical particles of actinides is under study. In fact, the handling of spherical particles could reduce the production of contaminant powder. In this context, sol-gel routes are under investigations and could offer the possibility to access to very homogenous compounds and interesting microstructures. This study describes preliminary works led in order to synthesise mixed compounds including minor actinides by internal gelation. According to the numerous parameters, the comparison of the two chemical systems U(IV)/Np(IV)/Pu(III)/Am(III)/Cm(III) and U(VI)/Np(V)/Pu(IV)/Am(III)/Cm(III) has been investigated by a study of systems including only two actinides or simulating elements.We studied first the influence of the initial broth composition on the gel microspheres structure. The results pointed out the necessity of controlling the hydrolysis kinetics to avoid the apparition of important cracks or deformations.Systematic experiments led on simulated actinides underlined that HMTA and urea quantities are essential parameters to control the gelation rate: for Zr(IV)/Y(III)/Ce(III), optimized HMTA/Me and urea/Me ratios were defined to obtain gel microspheres without major defects. Moreover, this study quantifies the influence of additives quantities and cation concentration on the gel microspheres microstructure.Furthermore, by comparing the two systems U(VI)/Pu(IV) and U(IV)/Pu(III), gelation experiments highlights the importance of the oxidation state of the cations. Increasing the amounts of Pu(III) led to modify broth composition to compensate the weak hydrolysis ability of the trivalent cation. In particular, this study put forward the importance of a high actinide concentration and a low NO3-/An ratio to favour hydrolysis reactions.The temperature of the gelation bath is also linked to the reactions kinetics. With Me(IV)/Me(III) systems, a temperature around 85°C seems to be a good compromise to avoid too violent gelation rates and to obtain sufficient hydrolysis to solidify the microspheres. As expected, this temperature range depends on the broth composition and especially on the nature and the oxidation state of metallic cations.After gelation, washing and drying steps, gel microspheres thermal treatment were studied using optical microscopic observations, thermogravimetric analysis and X-ray diffraction analysis. After calcination, the shape is globally preserved even if some cracks can still appear in non optimized conditions for systems including trivalent actinides (or their simulants). Whatever the system studied, XRD characterisations after treatment at 900°C underline the existence of solid solutions. Homogenous oxide solid solutions including U and Pu were particularly obtained: (U, Pu)O2 from the U(IV)/Pu(VI) system and probably a sub-stœchiometric one from the U(IV)/Pu(III) system.
12:30 PM - OO9.4
The Nature of PuO2+x: Oxide or Hydroxide Nonstoichiometry?
Mark Levy 1 , Christopher Stanek 2 , Robin Grimes 1
1 Materials, Imperial College London, London United Kingdom, 2 MST-8, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractIt is necessary to understand the structure and properties of actinide oxides for their optimum deployment. Nearly 50 years ago Drummond and Welch reported the first preparations of fluorite structured plutonium dioxides as a corrosion product on Pu metal with apparent oxygen excess stoichiometries from 2.04 to 2.06. Since this initial finding, others have found that in a moist, oxidising environment, PuO2 can assume higher metal to oxygen ratios and some evidence has even been presented to suggest that the stoichiometry extends as far as PuO3. Thus, limited hyperstoichiometry was observed in dry conditions and more pronounced deviations occurred in the presence of water.It is important to understand the mechanism by which hyperstoichiometric compositions can be formed because it governs the corrosion behaviour of plutonium in air, and in particular, the moisture enhanced corrosion in moist air. The stoichiometric behaviour is thus an important consideration when establishing procedures for the safe handling and storage of the actinide material.The mechanism accommodating PuO2+x hyperstoichiometry has been debated in the literature. There are two key discussion points: (1) the manner in which oxygen is accommodated in the lattice, i.e. as an oxide ion (O2- or O-) or as a hydroxide ion (OH-), and (2) the method of charge balance within the unit cell, i.e. is the Pu cation (IV), (V), or (VI)? If the structure of hyperstoichiometric PuO2+x derives strictly from oxygen ions, the composition eventually becomes Pu4O9. If, however, the nonstoichiometry is due to hydroxide accommodation, the composition becomes Pu4O8OH.Here, atomistic scale computer simulations based upon the Born model of the crystal lattice will be used to assess the relative energetics and unit cell parameter changes for different oxygen/hydroxide incorporation mechanisms. The results will be compared to previous experimental studies, for example to experiments by Haschke, Conradson and Penneman and computational results by Petit.
12:45 PM - OO9.5
Soft X-ray Scanning Transmission X-ray Microscopy (STXM) Spectromicroscopy of Actinides.
David Shuh 1 , Tolek Tyliszczak 2 , Peter Nico 3
1 Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Advanced Light Source Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractScanning transmission x-ray microscopy (STXM) spectromicroscopy at the Advanced Light Source Molecular Environmental Science (ALS-MES) Beamline 11.0.2 has been utilized to investigate actinide materials and particulates. The ALS-MES STXM utilizes near-edge x-ray absorption fine structure (NEXAFS) at the actinide 4d core level edges (700 eV to 900 eV) to obtain direct spectroscopic information from a range of actinide materials. The STXM is capable of imaging particles in several modes and collecting NEXAFS spectra, both with a spatial resolution better than 30 nm at this time. An important characteristic of the ALS-MES STXM is the capability to directly probe low Z element K-edges by NEXAFS, such as the oxygen and nitrogen K-edges, that are frequently key constituents of actinide materials. The safety precautions for STXM investigations of actinides require sealed encapsulation of the actinide materials between two thin silicon nitride windows with the actinide being distributed between the windows as particulates. This attainable level of experimental safety makes STXM an efficient method for collecting NEXAFS spectra The results from early studies of model, light actinide oxides will be presented, demonstrating the experimental capabilities and limitations of soft x-ray STXM spectromicroscopy for investigations of actinide materials. The spectroscopic results from recent transuranic STXM investigations of plutonium and curium complexes, along with their light element constituents, will be presented and interpreted. The imaging capabilities of STXM provide a unique means to observe the morphology of actinide and actinide-containing particulates, even when fully-hydrated, at a level that approaches the nanoscale. The results from several actinide, radionuclide, and lanthanide (used as a surrogate or for a direct comparison to actinide behavior) experiments including those focused on elucidating fundamental bonding characteristics and of environmental interests, will also be highlighted.However, the are some drawbacks of actinide soft x-ray STXM spectromicroscopy and in particular, the need to work at the actinide 4d edges imposes cross-sectional sensitivity requirements that makes low concentration work difficult without actinide agglomeration or clustering. This also complicates and makes sample preparation difficult. The potential of STXM for future studies of actinide particulates, colloidal materials, and in biogeochemical systems will be critically discussed.
OO10/MM10: Joint Session: Magnetic Resonance Studies on Actinides
Session Chairs
Julie Herberg
Bruce McNamara
Wednesday PM, November 29, 2006
Liberty (Sheraton)
2:30 PM - **OO10.1/MM10.1
NMR Spectroscopy and the Testing of Ab Initio Relativistic Electronic Structure Theory: Recent Results for Uranyl Salts.
Herman Cho 1 , Wibe de Jong 2 , Chuck Soderquist 3 , Bruce McNamara 3
1 Fundamental Science Directorate, Pacific Northwest National Laboratory, Richland, Washington, United States, 2 Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington, United States, 3 Environmental Technology Directorate, Pacific Northwest National Laboratory, Richland, Washington, United States
Show Abstract3:00 PM - **OO10.2/MM10.2
A 23Na and 133Cs MAS NMR Study of the Structural Transformations of Microcrystalline MxWO3+x/2.ZH2O Hexagonal Tungsten Bronze and NaW2O6.2H2O Cubic Tungsten Pyrochlore Systems.
John Hanna 1 , Victor Luca 1 , Christopher Griffith 1 , Kevin Pike 1 , Andrew Howes 2 , Mark Smith 2 , Thibault Charpentier 3
1 Institute of Materials Science & Engineering, ANSTO, Menai, New South Wales, Australia, 2 Dept. of Physics, University of Warwick, Coventry , Warwickshire, United Kingdom, 3 Laboratoire de Structure et Dynamique par Résonance Magnétique, Commissariat à l’Energie Atomique , Saclay France
Show AbstractLow temperature (25-600 oC) thermal transformation in hydrothermally-prepared microcrystalline hexagonal tungsten bronze compounds (AxWO3.2H2O where A is an exchangeable cation located in hexagonal channels of the structure) are studied as a function the exchangeable tunnel cation composition. Thermal treatments in air were studied using conventional laboratory-based X-ray diffraction while vacuum heating was studied by synchrotron X-ray diffraction and neutron diffraction. For the sodium form of the bronze, cell volume contraction occurs from room temperature to about 350 oC; this is the regime in which water is squeezed from the tunnel sites. This is followed by a cell volume expansion throughout the 350–600 oC temperature range. Over this entire temperature range studied a net thermal contraction in cell volume is observed due to anisotropic variations in the cell dimensions in which the c-dimension contracts more than the concomitant expansion in the a-direction. These changes explain why Cs+ ions are locked into tunnel positions at temperatures as low as 400 oC resulting in a significant reduction in extractability in nitric acid. While similar effects are observed for the as-prepared Na+-exchanged sample, the smaller radius of this cation causes it to be relatively easily removed under corresponding acidic conditions. 23Na MAS and MQMAS NMR have been used to investigate the sodium speciation and local order/disorder phenomena induced in the channel sites of the unsubstituted Na-tungsten bronze via a dynamic equilibrium with intercalated H2O and OH-. The speciation changes with thermal transformation and eventual phase transition over the 25-600 oC temperature range reported. Similarly, 23Na and 133Cs MAS NMR has been used to investigate the same phenomena in the Cs-substituted Na-tungsten bronze. These results corroborate the observations from quantitative Cs uptake measurements that the theoretical maximum Cs uptake in these systems is never achieved, and that the residual Na speciation after Cs incorporation demonstrates significantly increased short-range positional order. Low temperature thermal transformations in the hydrothermally-prepared microcrystalline defect pyrochlore system NaW2O6.2H2O have also been studied. In contrast, the zig-zag pseudo-tetrahedral channel sites of this structure afford very little discernable order with respect to Na speciation within these channels. 23Na MAS and MQMAS NMR studies show that some dynamic equilibrium between Na+ and H2O/OH- channel species also exists in similar fashion to the hexagonal W-bronze system, however, the overall complexion of the Na speciation is quite different from that of the hexagonal W-bronze. Preliminary investigations of Cs uptake and retention in the thermally treated defect pyrochlore (~600 oC) showed that very favourable Cs leach characteristics can be achieved with this system.
4:00 PM - OO10/MM10
BREAK
4:30 PM - **OO10.4/MM10.4
Identifying and Quantifying Actinide Radiation Damage in Ceramics with Radiological Magic-Angle Spinning Nuclear Magnetic Resonance.
Ian Farnan 1 , Herman Cho 2 , William Weber 2
1 Earth Sciences, Cambridge University, Cambridge United Kingdom, 2 EMSL, Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractIn the characterisation of amorphisation or local disordering due to actinide radiation damage, nuclear magnetic resonance (NMR) spectroscopy is attractive because it is element specific and equally sensitive to local structure in crystalline and amorphous materials. We have applied high-resolution solid-state NMR spectroscopy (magic-angle spinning) to radiation damaged natural minerals containing 238U/232Th to determine the ‘number fraction’ of amorphous material (fa) through spin-counting techniques. In samples with a known alpha dose, the number of atoms displaced per alpha decay may be determined from an integration of the spectrum. We have developed a protocol for performing similar magic-angle spinning experiments on plutonium containing ceramic samples with an activity of > 5 GBq. Results obtained have allowed data from ancient, radiation damaged mineral samples of ZrSiO4 (238U/232Th) to be compared with modern 238/239Pu doped ceramic ZrSiO4 samples. The number of atomic displacements per alpha particle from 239Pu is similar to that for 238U/232Th (4980 ± 300/α). At lower α-doses there are significant differences in the amorphous volume fraction (observed by density and x-ray diffraction) and the number fraction of displaced atoms (as measured by NMR) as a function of cumulative dose. These differences arise from local density considerations that manifest themselves in the local structure of the amorphous and crystalline phases. Using ab initio simulations of the damaged crystalline and amorphous regions, the magnetic response of these structures and hence the NMR shifts can be compared with experiment to reveal the nature of radiation induced changes occurring at the local scale.
5:00 PM - **OO10.5/MM10.5
A Review of the Contributions of Electron Paramagnetic Resonance Spectroscopy to Actinide Science.
Lynn Boatner 1
1 MSTD, Oak Ridge National Lab., Oak Ridge, Tennessee, United States
Show Abstract5:30 PM - **OO10.6/MM10.6
Rotating Microdetectors for Nuclear Magnetic Studies of Radioactive Materials.
Dimitris Sakellariou 1
1 DSM/DRECAM/SCM/LSDRM, CEA-Saclay, Gif-sur-Yvette France
Show Abstract