Alpha spectrometric evaluation of SRM-995 as a potential uranium/thorium double tracer system for age-dating uranium materials
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Uranium-233 (t 1/2 ~ 1.59E5 years) is an artificial, fissile isotope of uranium that has significant importance in nuclear forensics. The isotope provides a unique signature in determining the origin and provenance of uranium-bearing materials and is valuable as a mass spectrometric tracer. Alpha spectrometry was employed in the critical evaluation of a 233U standard reference material (SRM-995) as a dual tracer system based on the in-growth of 229Th (t 1/2 ~ 7.34E3 years) for ~35 years following radiochemical purification. Preliminary investigations focused on the isotopic analysis of standards and unmodified fractions of SRM-995; all samples were separated and purified using a multi-column anion-exchange scheme. The 229Th/233U atom ratio for SRM-995 was found to be 1.598E−4 (±4.50 %) using recovery-corrected radiochemical methods. Using the Bateman equations and relevant half-lives, this ratio reflects a material that was purified ~36.8 years prior to this analysis. The calculated age is discussed in contrast with both the date of certification and the recorded date of last purification.
KeywordsAge-dating Alpha spectrometry Nuclear forensics Uranium SRM-995 Thorium
This research was supported by the U.S. Departments of Homeland Security and Defense through the Nuclear Forensics Graduate Fellowship Program and a grant from the U. S. Department of Energy for the University of Cincinnati Nuclear Forensics Graduate Academic Program. The Department of Homeland Security sponsored the production of this material under DOE Contract Number DE-AC09-08SR22470 for the management and operation of Savannah River National Laboratory.
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