The detection and screening of plutonium in environmental samples is critical for nuclear forensics and nonproliferation efforts. Direct measurement of waterborne plutonium is challenging due to its low solubility. Techniques for isolating and concentrating plutonium for isotopic screening are time-consuming and often have to be performed offsite. The ability to perform rapid, onsite analysis of plutonium in aqueous sources would be a powerful nuclear forensics tool, but currently no such technology exists. In this study, we investigated the use of functionalized polymer thin films for the extraction and isotopic screening of waterborne plutonium via alpha spectroscopy. Polymer-ligand films were prepared by casting polystyrene and Pu-binding ligands onto 30 mm diameter silicon wafers through spin coating. This method of film casting provided a high-degree of control over the thickness and surface uniformity. Three polymer-ligand combinations were compared for their ability to capture plutonium from water at low and circumneutral pH, and the plutonium recovery and isotope peak resolution were determined for films with thicknesses from 25 to 250 nm. Plutonium uptake studies were performed by exposing the polymer-ligand samples for 3 h to 0.5 mL of a 242Pu solution, followed by a wash step to remove unbound plutonium from the surface. Isotope peak resolutions given as full width at half maximum (FWHM) for the samples containing di(2-ethylhexyl) phosphate, thenoyltrifluoroactetone, and dibenzoylmethane were measured to be 30-60 keV. At pH 2, only the films loaded with di(2-ethylhexyl) phosphate showed significant plutonium uptake ranging from 22 to 35%. Unexpectedly, FWHM and plutonium recoveries did not correlate with film thickness. Additional results will be presented from subsequent measurements designed to test the hypothesis that plutonium is isolated primarily at the polymer film-solution interface due either to slow diffusion through the film or accumulation of the ligands at the interface. These include results from tests performed at longer exposure times and circumneutral pH, along with spectroscopic measurements to quantify interfacial ligand concentrations.

Functionalized polymer thin films for plutonium capture and isotopic screening from aqueous sources

2019 Fall National Meeting

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