Focus Area 2(b) Advanced Characterization Methods
Led by Stosh Kozimor
The goal of the Advanced Characterization Thrust Area is to develop insight into how electronic structure and covalent bonding influence the chemical separations associated with plutonium and the other transplutonium actinides. To achieve this at Los Alamos National Laboratory (LANL) and the Stanford Synchrotron Radiation Lightsource (SSRL), we have combined our expertise in actinide radiochemistry and X-ray Absorption Spectroscopy (XAS) with the computational and synthetic expertise throughout the CAST network. This involves collaboration with the LANL CAST Computational Group to use XAS data alongside DFT theory calculations to characterize electronic structure and bonding in actinide compounds, complexes, and solutions of relevance to capturing, storing and reprocessing legacy nuclear materials.
X-ray absorption spectroscopy (XAS) is an in-situ element-specific technique that provides speciation and structural information on an element of interest. XAS data consist of two spectral regions: The X-ray absorption near-edge structure (XANES) provides quantitative information on oxidation state (including mixed-valent systems) as well as sensitivity to coordination, while the extended X-ray absorption fine structure (EXAFS) region provide information on the local structural environment. In addition, XAS spectra mix linearly and may be used to quantify species abundances in mixed-phase systems, with fractional sensitivities on the order of 1-3 mol%. The crystallinity of solid phases does not affect the sensitivity of XAS, and this method is thus ideal for characterizing amorphous, nanocrystalline and disordered materials as well as molecular species (e.g., solution or surface complexes) for which structural information cannot be obtained via conventional X-ray diffraction methods.
Los Alamos National Laboratory, located a short distance northwest of Santa Fe, New Mexico, enhances national security by ensuring the safety and reliability of the U.S. nuclear stockpile, developing technologies to reduce threats from weapons of mass destruction, and solving problems related to energy, environment, infrastructure, health, and global security concerns. The facilities for safely handling highly radioactive actinide elements are world class at LANL. LANL-CAST personnel have user access to the Stanford Synchrotron Radiation Lightsource a user facility operated for the U.S. Department of Energy (DOE) by Stanford University, Menlo Park, California. SLAC is a multi-program national laboratory exploring frontier questions in photon science, astrophysics, biochemistry, material science, particle physics and accelerator research. SLAC engages in fundamental research and is working to address some of the most pressing challenges of our time. SSRL produces extremely bright x-rays as a resource for researchers to study our world at the atomic and molecular level. SSRL provides unique educational experiences and serves as a vital training ground for future generations of scientists and engineers.