Uranium age determination by measuring the (230)Th/(234)U ratio

• Published in: Journal of radioanalytical and nuclear chemistry Vol. 264; no. 2; pp. 423 - 427
• Main Authors: LaMont, S P, Hall, G
• Format: Journal Article
• Language: English
• Published: 01-05-2005
• ISSN: 0236-5731
• DOI: 10.1007/s10967-005-0732-7

A radiochemical isotope dilution mass spectrometry method has been developed to determine the age of uranium materials. The amount of (230)Th activity, the first progeny of (234)U, that had grown into a small uranium metal sample was used to determine the elapsed time since the material was last radiochemically purified. To preserve the sample, only a small amount of oxidized uranium was removed from the surface of the sample and dissolved. Aliquots of the dissolved sample were spiked with (233)U tracer and radiochemically purified by anion-exchange chromatography. The (234)U isotopic concentration was then determined by thermal ionization mass spectrometry (TIMS). Additional aliquots of the sample were spiked with (229)Th tracer, and the thorium was purified using two sequential anion-exchange chromatography separations. The isotopic concentrations of (230)Th and (232)Th were determined by TIMS. The lack of any (232)Th confirmed the assumption that all thorium was removed from the uranium (230)Th and sample at the time of purification. The (23)Th and (234)U mass concentrations were converted to activities and the (230)Th/(234)U ratio for the sample was calculated. The experimental (230)Th/(234)U ratio showed the uranium in this sample was radiochemically purified in about 1945.