Local 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 5f features observed in photoelectron spectroscopy.

Pu(Am) is stable in the fcc δ-phase from a few atomic percent to nearly 80 atomic percent Am, expanding the average interatomic separation as the alloy concentration of Am increases. Both Pu and Am spontaneously decay by α-emission creating self-damage in the lattice in the form of vacancy-interstitial pairs and their aggregates. At sufficiently low temperatures, the damage is frozen in place, but can be removed by thermal annealing at sufficiently high temperatures, effectively resetting the system to an undamaged condition. The magnetic susceptibility and magnetization are observed to increase systematically as a function of accumulated damage in the fcc δ-Pu(1-x)Am(x) (x=0.224). Some results of these observations are reported here.

Auto radiolysis of uranium (VI) carbonate solutions between pH 5.9 and 7.2 is shown to alter the uranium speciation over relatively short periods of time and was followed by 13C NMR and visible spectrophotometry, using dissolved [233(UO2)3(CO3)6]6- both as the radiolysis source (DÑ= 14.9 Gy/hr) and as a trap for the newly formed hydrogen peroxide. The speciation is different than the uranyl mixed peroxy carbonate species that have been reported for higher pH carbonate solutions.

The electronic structure of single crystal UO2 and polycrystalline δ-Pu is examined using photoelectron spectroscopy. These two actinide materials exhibit properties consistent with the 5f electrons at the threshold between localized and itinerant character. The results for δ-Pu may be viewed as the 5f electrons exhibiting a dual nature with some fraction of the 5f levels localized and not participating in the bonding while the other fraction of 5f character is involved in bonding and hybridization with the conduction electrons. For UO2 where angle-resolved photoemission is available, one observes dispersion in the 5f features indicative of the 5f electrons being influenced by the periodic potential of the lattice rather than purely influenced by the site to which the 5f electrons are generally localized.

X-Ray Absorption Spectroscopy (XAS) and Photoelectron Spectroscopy (PES) have been performed upon highly radioactive samples, particularly Plutonium, at the Advanced Light Source in Berkeley, CA, USA. First results from alpha and delta Plutonium are reported as well as a detailed analysis of sample quality.

The hydrolysis chemistry of the tetravalent actinides is discussed based on recent studies with thorium. The coupling of high energy x-ray scattering and single crystal diffraction has provided insight into the structures of the polynuclear complexes formed by hydrolytic reactions of the tetravalent actinides. The success of these experiments with thorium presents many opportunities for the elucidation of the structures and thermodynamic quantities describing the dissolved polynuclear complexes of the heavier actinides.

In this work, we have undertaken to follow the evolution of the PuCoGa5 superconducting behavior as a function of the damages created by self-radiation effects induced from the Pu-decay. It is shown that the critical temperature is particularly sensitive with ageing. Ageing effects on fundamental parameters such as the lattice parameters of the PuCoGa5 and the electrical resistivity provide some new hints of the unconventional character of the superconductivity in this class of materials

Fano Effect measurements are the key to direct observation of the Kondo or spin shielding intrinsic to models of electron correlation. The Fano Effect is the observation of spin polarized photoelectron emission from NONMAGNETIC materials, under chirally selective excitation, such as circularly polarized photons. Below are described three spectrometers, with which Fano Effects measurements have been made.

We present changes in volume, immersion density, and tensile property observed from accelerated aged plutonium alloys. Accelerated alloys (or spiked alloys) are plutonium alloys enriched with approximately 7.5 weight percent of the faster-decaying 238Pu to accelerate the aging process by approximately 17 times the rate of unaged weapons-grade plutonium. After sixty equivalent years of aging on spiked alloys, the dilatometry shows the samples at 35°C have swelled in volume by 0.15 to 0.17 % and now exhibit a near linear volume increase due to helium in-growth. The immersion density of spiked alloys shows decrease in density, similar normalized volumetric changes (expansion) for spiked alloys. Tensile tests show increasing yield and engineering ultimate strength as spiked alloys are aged.

We report Fermi surface and magnetic properties of a cubic PuIn3 grown by the indium flux method. Fermi surfaces detected by the de Haas-van Alphen effect can be well explained by the band calculations assuming itinerant 5f electrons.

The results of our recent neutron scattering studies on actinide ‘115’ compounds are reviewed. The itinerant many-body f-electron system and cross over to the localized character are realized only in actinide system. Actinide ‘115’ family is very interesting, because we can grow high quality single crystals of many iso-structural compounds with different number and character of f electrons and valence d electrons. Variety of the ground state have been reported, e.g. paramagnetic, itinerant magnetism, and heavy fermion superconductivity in PuCoGa5. Very recently we have intensively studied the magnetic structure in UTGa5 and NpTGa5, These compounds exhibit a variety of the magnetic structure with A-, C-, G-type antiferromagnetic and ferromagnetic ordering and canted structure. NpFeGa5 exhibits an unusual magnetic anisotropy with the direction of the magnetic moment inclined about 25 degrees from the tetragonal basal plane. On the other hand, the localized compounds RRhIn5 (R: Tb, Ho, Dy, Nd) shows the antiferromagnetic structure with q=(1/2 0 1/2). The magnetic moment is parallel to the c-axis. An identical magnetic structure in rare earth compounds is a consequence of the localized nature of 4f electrons. We found that NpFeGa5, NpNiGa5, and NpRhGa5 exhibit 5f electronic transition between the low- and high-moment states associated with a change in the direction of the magnetic moment. The diverse magnetic ordering and the 5f electronic transition suggest that the orbital degree-of-freedom of itinerant 5f electrons may play important role for the physical properties in many body f-electron systems. Actually a localized model predicts the magnetic structure and the phase diagram with magnetic and quarupolar order parameters. A resonant X-ray scattering study is in progress, if the predicted antiferroquadrupole order coexists with the canting antiferromagnetic dipole order in NpNiGa5.

Core-level and valence-band spectra of Pu and the other early actinide compounds show remarkable systematics, which can be understood in the framework of final state screening. We compare the early actinide (U, Np, Pu and Am) metals, nitrides and hydrides and a few other specific compounds (PuSe, PuS, PuCx, PuSix) prepared as thin films by sputter deposition. In choosing these systems, we combine inherent 5f band narrowing, due to 5f orbital contraction throughout the actinide series, with variations of the chemical environment in the compounds. Goal of this work was to learn more on the electronic structure of the early actinide systems and to achieve the correct interpretation of their photoemission spectra. The highly correlated nature of the 5f states in systems, which are on the verge to localization, makes this a challenging task, because of the peculiar interplay between ground state DOS and final-state effects. Their influence can be estimated by doing systematic studies on systems with different (5f) bandwidths. We conclude on the basis of such systematic experiments that final-state effects due to strong e-e correlations in narrow 5f-band systems lead to multiplet like structures, analogous to those observed in the case of systems with localized electron states. Such observations in essentially band-like 5f-systems was first surprising, but the astonishing similarity of photoemission spectra of very different chemical systems (e.g. PuSe, Pu2C3 and δ-Pu) points to a common origin, relating them to atomic features rather than material dependent density of states (DOS) features.

This is an exciting time to be involved in plutonium metallurgical research. Over the past few years, there have been significant advances in our understanding of the fundamental materials science of this unusual metal, particularly in the areas of self-irradiation induced aging of Pu, the equilibrium phase diagram, the homogenization of δ-phase alloys, the crystallography and morphology of the α'-phase resulting from the isothermal martensitic phase transformation, and the phonon dispersion curves, among many others. In addition, tremendous progress has been made, both experimentally and theoretically, in our understanding of the condensed matter physics and chemistry of the actinides, particularly in the area of electronic structure. Although these communities have made substantial progress, many challenges still remain. This brief overview will address a number of important challenges that we face in fully comprehending the metallurgy of Pu with a specific focus on aging and phase transformations.

Ab initio calculations using SCF approach for and analysis of results of investigation of the electronic structure of the clusters RA+n:[L]k with rare earths or actinides were carried out for the clusters in solids and liquids. Theoretical results for the electronic structure, radial integrals and energy of X- ray lines are presented for AC ions with unoccupied 5f-shell in the clusters in oxides, chlorides and fluorides environment. Possibility of collaps of nf-shell for the separate clusters and identification of electronic state of ions with unstable nuclei, are discussed, too.

Microhardness testing and transmission electron microscopy are used to study the effects of long-term service on the aging behavior of a water-quenched U-6wt.% Nb alloy when subjected to isothermal aging at 200°XC. The original α''c phase in the WQ-U6Nb alloy is found to become partially ordered over 18 years of aging at ambient temperatures, i.e., natural aging, forming a microstructure that is featured by antiphase domain boundaries (APBs). When subsequently aged at 200 °C, an ordered phase U3Nb is precipitated through a nucleation-and-growth mechanism, suppressing spinodal decomposition that occurs when the water-quenched alloy is artificially aged at the same temperature. The different phase transformation paths lead to different microhardness changes during artificial aging: the naturally aged alloy is more slowly hardened, but to a greater microhardness peak value.

Uranium is an extremely important material for commercial and military applications (i.e. nuclear power, nuclear weapons, conventional weapons, and armor systems) and, like a number of other materials, is vulnerable to corrosion by environmental gases that affect their properties, leading to component degradation, shortened lifetimes and materials failure. For uranium this is particularly true in the case of corrosion by hydrogen. A fundamental understanding of the corrosion process at the nucleation stage is of critical importance. The goal of this work is to study the role of common chemical impurities in uranium with initiation sites for the formation of destructive hydride blisters. Samples were implanted with various ions, annealed under vacuum at 200°C, than exposed to one atm of ultra-pure hydrogen. Scanning force microscopy surface potential imaging was used to characterize the structure and corresponding electrical properties of polycrystalline uranium surfaces that resulted from the implantation of different suspect atoms after exposure to hydrogen gas. Surface potential images revealed features related to different oxide structures and hydride spots/blisters as well as other features not obvious in the corresponding topograph. In the surface potential images, blisters appear as bright (higher potential) features in sharp contrast to the uranium oxide background. Often a possible inclusion was observed in the center of a blister. Blister formation did not appear to correlate with implantation of any specific specie, however, distinct differences were seen between implanted and non implanted sides of the same sample.

New ligands and materials are required that can coordinate, sense, and purify actinides for selective extraction and reduction of toxic, radioactive wastes from the mining and purification of actinides. 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. A detailed evaluation of the structure and bonding of actinide coordinating ligands like these is important for the design of new selective ligand systems. Knowing the difficulty with working with the crystals resulting from these ligand systems and safe handling considerations for working with Pu, procedures were developed that utilize the Advanced Light Source of Lawrence Berkeley National Laboratory to determine the solid-state structures of Pu complexes by X-ray diffraction.

The around-the-mean-field version of the LDA+U correlated band theory is applied to investigate the electronic and magnetic structure of δ-Pu, Am, their alloys and compounds. It gives correct non-magnetic ground state for Pu and Am, and provides a good agreement with experimental equilibrium volumes and bulk moduli. For Pu-Am alloys, despite a lattice expansion caused by the Am atoms, neither tendency to 5f localization nor formation of local

X-ray absorption spectroscopy and electron energy loss spectroscopy are complementary analytical techniques on energy and spatial resolution. These techniques are based on the same fundamental physical process of core excitation with either an incident photon or incident electron. In the proper experimental configuration the electron and photon inelastic scattering amplitudes are comparable and thus the x-ray and electron absorption edges look identical. We have applied these two complementary analytical techniques to investigate the electronic structure of C ion implanted U. Implantation of C+ ions into U238 has been shown to produce a physically and chemically modified surface layer that passivates the surface preventing further air oxidation and corrosion. Comparison of the resultant spectra reveal that transitions between the initial state and a series of final states yield numerous strong features at the absorption edge that can provide structural information and information on the local chemical environment, including the character of the U 5f state.

Specific heat of Pu doped with Am was studied for several Am concentrations (8-20%) ensuring the δ-Pu fcc structure. The results reveal that the γ value of the low temperature specific heat is lower than originally assumed (γ of 35 - 55 mJ/mol K2 can be deduced for Pu-8%Am) and does not increase with the Am-induced lattice expansion. The findings can be taken as an indication of the absence of the Pu-5f states at the Fermi level.