Development of Synchrotron-Based Analyses Techniques of Environmental Samples

Synchrotron facilities generate intense X-ray beams that can be focused down to micron and submicron probes to non-destructively study the chemical and structural properties of materials. Synchrotron-based microprobe techniques are used in a wide range of fields of study to provide spatially-resolved sample composition information. Here, we report on a multi-institutional effort to evaluate how synchrotron-based probes can support actinide analysis. This study made use of three different synchrotron radiation light sources operated by the US Department of Energy: the National Synchrotron Light Source-II (NSLS-II) at Brookhaven National Laboratory, the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory, and the Stanford Synchrotron Radiation Lightsource (SSRL) at SLAC National Accelerator Laboratory. Each of these light sources provides different capabilities, and these were evaluated using test samples of known actinide particulates embedded in collodion, a visually-transparent gel of nitrocellulose in ether and alcohol. These NNSA-funded studies focused on determining the chemical composition and oxidation state of uranium-containing particles, with an emphasis on throughput, spatial resolution, and sensitivity. The results show that synchrotron X-ray fluorescence microscopy and micro-spectroscopy complement current laboratory-based techniques while preserving the samples for subsequent isotopic analysis. Synchrotron radiation probes at the NSLS-II can scan particles at a resolution of 1 micron in a few minutes, with detection limits below 10 ppm for elements from Ti to U. With smaller step sizes, a resolution of 0.5 microns can be obtained to more clearly reveal intra-particle heterogeneity. X-ray absorption spectroscopy at the uranium L3 edge generated unique fingerprints for each particle type, depending on oxidation state and local chemical environment. Studies at the ALS showed a promising new technique to rapidly conduct wide-area scans to locate U-containing particles. In addition, X-ray fluorescence measurements at the ALS utilized a new experimental chamber to enable the detection of elements as light as fluorine. The next phase of this study is to further streamline data acquisition, data reduction, and reporting so that the advantages of rapid synchrotron radiation-based analysis can be optimally harnessed. In addition, there is the potential to incorporate rapid non-destructive structural analysis of particles based on synchrotron-enabled micro-diffraction analysis.