High Yield Fission Product Separations and Quantification For Nuclear Forensic Applications
Swearingen, Kevin John
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Strontium-90 and its daughter, yttrium-90, have cumulative fission yields of approximately 6 percent from the thermal neutron induced fission of uranium-235. With these high yields, Sr and Y are prevalent following an accidental release or a nuclear detonation. Strontium-90 has a half-life of 28.8 years; accordingly, both it and 90Y will continue to be present in the environment for several centuries following a release. The relatively long half-life and high yields make 90Sr and 90Y useful isotopes for nuclear forensics. Due to chemical similarities, ingested 90Sr can replace Ca within the structure of bone, leading to an increased health risk. The long half-life and health risk requires 90Sr environmental monitoring for public health concerns. Due to 90Sr and 90Y being quantified by their β- emissions, traditional quantification methods require substantial separations or wait times (approximately 3 weeks) before quantification can be completed. In both public health and nuclear forensics, lengthy wait times for accurate quantifications are never desirable. This body of work characterizes separation techniques and develops improved quantification methods for Sr and Y. Solid phase extractions are typically utilized for the quantification of 90Sr and 90Y in case public health and nuclear forensics monitoring. The two primary commercial Sr resins were compared under identical conditions to gauge which product was the most effective at isolating Sr. Improved novel use of inductively coupled plasma optical emission spectrometry techniques were developed to improve quantification methods for complex solutions without increasing sample processing time or costs. A new technique was developed to simultaneously determine 90Sr and 90Y activities via liquid scintillation counting to reduce the time required to obtain the individual activities from 3 weeks to 1 week without a decrease in precision.