(50f) Synthesis and Characterization of Extractive Scintillating Resin for Ultra-Trace-Level Quantification of Alpha- and Beta- Emitting Radionuclides in Environmental Waters

Traditional methods of quantifying alpha- and beta-emitting radionuclides in environmental water samples involve time-intensive, batch style analytical techniques that utilize bulky instruments.  A recent development in environmental sensing is a portable, flow cell detector that utilizes extractive scintillating resin.  The extractive scintillating resin serves the dual purpose of (1) concentrating the radionuclide of interest and (2) serving as a radiation transducer by transmitting a visible light-signal proportional to the radionuclide’s activity.  Currently, such resins are produced by physically absorbing organic extractants and fluorophores into a polymer matrix.  Unfortunately, this approach yields resins with poor stability as the active components leach from the resin over time. 

This contribution describes our work to synthesize a new class of extractive scintillating resin in which the fluorophore and the extractive ligand are bound covalently within the matrix.  Suspension polymerization was used to prepare porous poly[(4-vinyl toluene)-co-divinylbenzene-co-(4-vinylbenzyl chloride)] resin beads with 2-(1-naphthyl)-5-phenyloxazole as the fluorophore. The resin was functionalized with a uranium-selective bisphosphonate ligand through a nucleophilic substitution reaction and then hydrolyzed to its bis(phosphonic acid) form. It was characterized by FTIR to support functionalization, confocal laser scanning microscopy to observe the distribution of the fluorophore, and titrations to quantify the accessible binding sites. The binding capacity and uptake kinetics were investigated for both the bisphosphonate and bis(phosphonic acid) functionalized resins. Uranium uptake experiments were performed for both resins at pH values above and below the pK_a1 and pK_a2 of the phosphonic acid groups to evaluate the contributions that chelation and cation exchange make to overall uranium uptake.

The second function of the resin, the ability to serve as a radiation transducer, was evaluated.  The stability of the resin, with respect to luminosity, was tested by performing leaching experiments in which the extractive scintillating resin was exposed to consecutive volumes of either nitric acid or water.  The luminosity was measured before and after exposure by exposing a monolayer of resin to an alpha-emitting source and measuring the luminosity with a photomultiplier tube. In addition, confocal laser scanning microscopy was used to visualize the cross-sectional fluorophore distribution profile within the resin as a function of leachant volume.  Finally, the overall resin performance was evaluated by static scintillation measurements in which the bound uranium initiated the scintillating event and the emitted photons were counted.  From these data, the detection efficiency of the resin was determined.  Findings from this research provide the foundation for a new class of chemically stable extractive scintillating resin for use in field-deployable environmental sensors.