(237h) Development of Polymer Sensors for the Online Detection of Waterborne Uranium

Nuclear nonproliferation efforts and treaty verification require portable, robust radiation detectors capable of detecting trace-levels of radionuclides in environmental matrices. A recent development in environmental sensing is a portable, flow cell detector that utilizes extractive scintillating resin. Extractive scintillating resin serves the dual purpose of (1) concentrating the radionuclide of interest and (2) serving as a radiation transducer. Previous resins were produced by physically absorbing organic extractants and fluors in a polymer matrix, which resulted in unstable resins as the active components leach from the polymer over time.

This contribution describes our work to synthesize a new class of extractive scintillating resin in which the fluor and the ligand are bound covalently within the polymer matrix. Two approaches have been taken to synthesize these resins: (1) synthesis of a 4-vinylbenzyl chloride containing polymer followed by solid-phase synthesis techniques to add the uranium-selective ligand and (2) one-pot polymerization utilizing a polymerizable fluor and ligand. In the first approach, suspension polymerization was used to prepare resin beads comprising 4-vinyltoluene; divinylbenzene; the fluor, 2-(1-napthyl)-4-vinyl-5-phenyloxazole; and the solid phase reactant, 4-vinylbenzyl chloride then the resin was functionalized with methylphosphonic acid. In the second approach, resins were prepared by suspension polymerization comprising 4-vinyltoluene; divinylbenzene; 2-(1-napthyl)-4-vinyl-5-phenyloxazole; and the ligand, ethyleneglycol methacrylate phosphate. Porosity of the resin was varied by using different dilutents during suspension polymerization and was analyzed by BET. Resins were characterized by Fourier-transform infrared spectroscopy to support functionalization. Fluorescence properties were studied with spectrofluorometry to measure emission wavelength and intensity. The detection efficiency of the resins in near neutral pH water was evaluated by sequentially loading uranium onto a resin-packed column followed by standard scintillation counting of the column. Resins synthesized by the first approach detected uranium-233 with an efficiency of 40% in pH 4, distilled water. The flow cell efficiency of the resins was evaluated in an online, flow-cell detector. Resins synthesized by the first approach showed 20% flow cell efficiency in pH 4, simulated ground water. Results from this research are laying the groundwork for the development of portable radiation sensors capable of online monitoring of waterborne alpha-emitting radionuclides.