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.

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.

One effect of pressure on elements and compounds is to decease their interatomic distances, which can bring about dramatic perturbations in their electronic nature and bonding, which can be reflected in changes in physical and/or chemical properties. One important issue in the actinide series of elements is the effect of pressure on the 5f-electrons. We have probed changes in electronic behavior with pressure by monitoring structure by X-ray diffraction, and have studied several actinide metals and compounds from thorium through einsteinium. These studies have employed angle dispersive diffraction using synchrotron radiation, and energy dispersive techniques via conventional X-ray sources. The 5f-electrons of actinide metals and their alloys are often affected significantly by pressure, while with compounds, the structural changes are often not linked to the involvement of 5 f-electron. We shall present some of our more recent findings from studies of selected actinide metals, alloys and compounds under pressure. A discussion of the results in terms of the changes in electronic configurations and bonding with regard to the element's position in the series is also addressed.

We have been investigating the spectroscopy of actinides in materials having relevance to nuclear waste management. Discussed here are the excitation and emission profiles of curium in high temperature borosilicate glasses, and pure halide compounds. Probing the local coordination environment of Cm(III) in these matrices has been one of the goals of this study. Comparison of the nephelauxetic effects indicate that the silicate matrix provides a more basic environment than either F− or Cl− surroundings found in pure compounds of curium. As a result, f - f transition energies are red shifted significantly in the silicate matrix as compared to that of the neat CmF3 system. Moreover, laser induced emissions have been noted with CmF4 after treatment at elevated temperatures. The higher energy spectral region, consisting of emission bands at 20100 and 16750, is assignable to f - f transitions in Cm(III), which is the expected thermal decomposition product. Energy transfer from Cm(III), followed by a second photon absorption is believed to be responsible for the strong emission bands at 12550, and 13580 cm−1. from presently unidentified emitting species. Results are discussed in relation to the oxidation state and fluorescence dynamics of actinide species in neat compounds, as well as in matrices being considered for waste immobilization.

Polycrystalline pyrochlore oxides consisting of selected f elements (lanthanides and actinides) and Zr and Hf have been prepared and characterized. Characterization to date has been primarily by X-ray diffraction, both at room and at elevated temperatures. Initial studies concentrated on selected lanthanides and the Np, Pu and Am analogs (reported here) but have been extended to the other actinide elements through Cf. Data from these studies have been used to establish a systematic correlation regarding the fundamental materials science of these particular pyrochlores and structurally related fluorite-type dioxides. In addition to pursuing their materials science, we have addressed some potential technological applications for these materials. Some of the latter concern: (1) immobilization matrices; (2) materials for transmutation concepts; and (3) special nuclear fuel forms that can minimize the generation of nuclear wastes. For f elements that display both a III and IV oxidation state in oxide matrices, the synthetic path required for producing the desired pyrochlore oxide is dictated by their pseudo-oxidation potential the stability of the compound towards oxygen uptake. For the f elements that display an oxidationreduction cycle for pyrochlore-dioxide solid solution, X-ray diffraction can be used to identify the composition in the oxidation-reduction cycle, the oxygen stoichiometry and/or the composition. This paper concentrates on the Np, Pu and Am systems, and addresses the above aspects, the role of the crystal matrix in controlling the ceramic products as well as discussingsome custom-tailored materials.

We have investigated certain aspects of the fundamental chemistry and materials science of the 4fand several 5f-elements in three glass matrices. Two of these matrices were high-temperature (850° and 1450°C melting points) silicate-based glasses and the third was a sol-gel glass. Optical spectroscopy was the principal investigating tool. One aspect of the work here was to ascertain the oxidation state exhibited by these elements in the different glasses, as well as the factors that control and/or may alter this state. An important finding was noting a general correlation between the oxidation states obtained in the two high-temperature glasses and those observed in the oxides of these elements. Of the twenty three f-elements considered here, only three exceptions (Ce, Am and Bk) or examples of variable behavior (Pr, Tb, U and Cf) to this correlation were noted. One explanation offered for the exceptions is based on the stability afforded by the oxides' fluorite lattice. The correlation also applied to the sol-gel glasses after they had been heated. Other oxidation states for some elements could be obtained in the sol-gel glasses prepared at 25°C. Presented here is a summary of the oxidation states observed for these elements in three glass matrices and how these states correlate with those observed in the oxides of these elements and with the relative oxidation potentials for the elements.

Aerogels are a class of colloidal materials which have high surface areas and abundant mesoporous structure. SiO2 aerogels show unique physical, optical and structural properties. When catalytic metals are incorporated in the aerogel framework, the potential exists for new and very effective catalysts for industrial processes. Three applications of these metal-containing SiO2 aerogels as catalysts are briefly reviewed in this paper — NOx reduction, volatile organic compound destruction, and partial oxidation of methane.

Spectroscopie properties of selected 4f-elements in a sol-gel and two high temperature silicate based glasses are reported. In particular, the spectral properties of the Eu3+ ion have been used to probe the local coordination environment of the f-elements in these glass matrices. Luminescence studies of the high temperature glasses indicated that the electric dipole allowed f-f transitions dominate the spectra which suggests that the local symmetry around the 4f-ions is low. Temperature-dependent spectroscopie studies of the sol-gel glasses indicated that the f-elements retain a “solution-like” environment prior to thermal processing. After heat treatment, an increase in the emission intensities of the electric-dipole transitions is accompanied by a concomitant decrease in the magnetic-dipole allowed transitions. Moreover, excited state interactions has also been observed in the high temperature glasses that contain certain multiple f-elements. In Pr-Sm systems, exclusive excitation of the Sm3+ ion with a 514 nm argon ion laser line provides a higher-energy emission band (ca. 490 nm) from the Pr3+ ion (3P0 → 3H4) transition. This energy up-conversion is attributed to energy transfer from the 6H13/2 level of the Sm3+ ion to the 3Hg6 state of the Pr3+ ion. Following a second photon absorption, the Pr3+ ion is excited to the emitting 3P0level.

We have pursued some of the fundamental chemistry and materials science ofamericium in three glass matrices, two being high-temperature (850° and1400°C melting points) silicate-based glasses and the third a sol-gel glass.Optical spectroscopy was the principal investigating tool in the studies.One aspect of this work was to determine the oxidation state exhibited byamericium in these matrices, as well as factors that control and/or mayalter this state. We have noted a correlation between the oxidation state ofthe f-elements in the two high-temperature glasses with theirhigh-temperature oxide chemistries. One exception was americium: althoughamericium dioxide is the stable oxide encountered in air, when this dioxidewas incorporated into the high-temperature glasses, only trivalent americiumwas found in the products. When trivalent americium was used to prepare thesol-gel glasses at ambient temperature, and after these products were heatedin air to 800°C, again only trivalent americium was observed. Potentialexplanations for the unexpected behavior of americium is offered in thecontext of its basic chemistry. Experimental spectra, spectroscopieassignments and other pertinent data obtained in the studies arediscussed.

Several oxidation states of neptunium and plutonium, Pu(III), Pu(IV),Pu(VI), Np(IV), Np(V), and Np(VI), were studied in glasses prepared by asol-gel technology. The oxidation state of these actinides in the sol-gelproduct was examined by absorption spectroscopy after solidification, aging,and thermal treatment. The oxidation state of the actinides in the startingsolutions was essentially maintained through the solidification process ofthe silica matrix. However, during densification and removal of residualsolvents at elevated temperatures, both actinides converted eventually totheir tetra valent states while in the different sol-gel products. Thisfinding is in accord with reports that tetravalent states of plutonium andneptunium are acquired in glass products prepared by dissolution of theactinide in molten glasses. Comparisons between room temperature spectraobtained from neptunium and plutonium in heated sol-gel products and frommolten glass products showed subtle differences that can be related to themetal ion's environments.

X-ray powder diffraction (XRPD) analysis has proven to be extremely valuable in the study of the transplutonium elements. The high specific activity and the thermal energy associated with the radioactive decay of einsteinium isotopes make XRPD analysis of einsteinium samples very difficult. The major problems are destruction of the samples crystallinity and alteration of their chemical composition. Blackening of the X-ray film also compromises the analyses. By applying certain guidelines given here, a limited amount of success has been achieved in obtaining diffraction data on einsteinium and some of its compounds.