The electronic structure of PuB6, an actinide analog of SmB6 , was investigated making use of a combination of the density functional theory (DFT), and the exact diagonalization (ED) of an effective discrete Anderson impurity model. Intermediate valence ground state with the f-shell occupation n4f =5.5 for the Pu atom in PuB6 is calculated. The 5f-shell magnetic moment is completely compensated by the moment carried by the electrons in the conduction band. Already in DFT, PuB6 is an insulator with a small amount of holes near the X-point, and the indirect band gap of ≈60 meV. This band gap becomes direct in DFT+ED calculations supporting the idea of “topological Kondo insulator” in PuB6. Connection between the electronic structure of PuB6 and δ-Pu is established. We propose that these materials belong to a new class of intermediate valence “Racah” materials with the multi-orbital “Kondo-like” singlet ground-state.

We have synthesized and investigated electronic properties of several non-centrosymmetric actinide compounds, which do not have an inversion center in the crystal structure “globally” or “locally”, under high pressure. The Néel temperature of an antiferromagnet UIrSi3 with “globally” non-centrosymmetric structure increases with increasing pressure at a rate of 2.5 K/GPa up to 5 GPa. On the other hand, T Ns of U2Rh3Si5 and U2Ir3Si5, which are “locally” non-centrosymmetric compounds, decrease with -1 K/GPa and -0.5 K/GPa with increasing pressure, respectively. Here, U2Ir3Si5 is a new antiferromagnet crystallizing in the U2Co3Si5-type of orthorhombic structure. Below T N = 36.5 K, U2Ir3Si5 shows magnetic order-order transition at T 0 = 26.1 K with a first-order nature. Electrical resistivity in U2Ir3Si5 shows semiconducting-like behavior due to the formation of the super-zone gap in the antiferromagnetic state. T N and T 0 as well as semi-conducting-like behavior in resistivity are suppressed by external pressure.

Several diverse types of UH3-based hydrides can be prepared by hydrogenation of bcc U-based alloys. Pair Distribution Function (PDF) analysis using high-energy X-rays identified that the (UH3)1-x Mox hydrides are nanocrystalline, with the structure motif based mainly on the β-UH3 structure. α-UH3 represents a minority component. On the other hand, PDF of the (UH3)1-x Zrx hydrides corresponds well to the α-UH3 crystal structure. All the hydrides are ferromagnetic, with the Curie temperature T C reaching up to 203 K.

High purity UO2 powder samples were subjected to accelerated aging under controlled conditions with relative humidity ranging from 34% to 98%. Characterization of the chemical speciation of the products was accomplished using X-ray photoelectron spectroscopy (XPS). A shift to higher uranium oxidation states was found to be directly correlated to increased relative humidity exposure. Additionally, the relative abundance of O2-, OH-, and H2O was found to vary with exposure time. Thus, it is expected that uranium oxide materials exposed to high relative humidity conditions during processing and storage would display a similar increase in average uranium valence.

Recent nuclear forensics cases have focused primarily on plutonium (Pu) and uranium (U) materials. By definition however, nuclear forensics can apply to any diverted nuclear material. This includes neptunium (Np), an internationally safeguarded material like Pu and U, that could offer a nuclear security concern if significant quantities were found outside of regulatory control. This case study couples scanning electron microscopy (SEM) with quantitative analysis using newly developed specialized software, to evaluate a non-traditional nuclear forensic sample of Np. The results of the morphological analyses were compared with another Np sample of known pedigree, as well as other traditional actinide materials in order to determine potential processing and point-of-origin.

We employ a combination of the density-functional theory and the dynamical mean-field theory to study the electronic structure of selected rare-earth sesquioxides and dioxides. We concentrate on the core-level photoemission spectra, in particular, we illustrate how these spectra reflect the integer or fractional filling of the 4f orbitals. We compare the results to our earlier calculations of actinide dioxides and analyze why the core-level spectra of actinide compounds display a substantially reduced sensitivity to the filling of the 5f orbitals.

Metallographical examination of Uranium alloys can benefit from electron back scatter diffraction (EBSD) technique. Various methods of surface preparation for microstructural characterization are described and compared. The aim of the study was to optimize the preparation technique for surfaces of U alloy splats for EBSD mapping, particularly in the context of U1-x Mox alloys, as properties of γ-U surfaces (e.g. with more Mo) are very different than for mostly α-U type (low-alloyed U).

Plutonium metal is a very unusual element, exhibiting six allotropes at ambient pressure, between room temperature and its melting point, a complicated phase diagram, and a complex electronic structure. Many phases of plutonium metal are unstable with changes in temperature, pressure, chemical additions, or time. This strongly affects structure and properties, and becomes of high importance, particularly when considering effects on structural integrity over long periods of time [1]. This paper presents a time-dependent neutron total scattering study of the local and average structure of naturally aging δ-phase 239Pu-Ga alloys, together with preliminary results on neutron tomography characterization.

Having worked on several approaches to CO2 capture over the past decade, we have studied a great number of physical and chemical solvents as well as polymer and composite membranes. Initially, most of these materials were based upon ionic liquids (ILs), however due to challenges encountered in applying ILs to meet the demanding requirements in CO2 separation processes, there is a need to reconsider what role (if any) ILs might play in CO2 capture technologies. Ultimately, more promising and robust materials will not come from ILs themselves, but from retrosynthetic analysis and a reconsideration of which structural variables and properties are (and are not) important. The hybridization of the constituent parts into entirely new, yet seemingly familiar substances, can yield greatly improved properties and economics. This manuscript highlights recent work from our group based on lessons learned from ILs that have spurred the development of new amine solvents and polymer materials to better address the demanding process conditions and requirements of CO2 capture and related separations.