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Uranium age determination by measuring the <Superscript>230</Superscript><Superscript> </Superscript>Th/<Superscript>234</Superscript>U ratio

Article

Summary

A radiochemical isotope dilution mass spectrometry method has been developed to determine the age of uranium materials. The amount of <Superscript>230</Superscript> Th activity, the first progeny of <Superscript>234</Superscript>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 <Superscript>233</Superscript>U tracer and radiochemically purified by anion-exchange chromatography. The <Superscript>234</Superscript>U isotopic concentration was then determined by thermal ionization mass spectrometry (TIMS). Additional aliquots of the sample were spiked with <Superscript>229</Superscript> Th tracer, and the thorium was purified using two sequential anion-exchange chromatography separations. The isotopic concentrations of <Superscript>230</Superscript> Th and <Superscript>232</Superscript> Th were determined by TIMS. The lack of any <Superscript>232</Superscript> Th confirmed the assumption that all thorium was removed from the uranium sample at the time of purification. The <Superscript>230</Superscript> Th and <Superscript>234</Superscript>U mass concentrations were converted to activities and the <Superscript>230</Superscript> Th/<Superscript>234</Superscript>U ratio for the sample was calculated. The experimental <Superscript>230</Superscript> Th/<Superscript>234</Superscript>U ratio showed the uranium in this sample was radiochemically purified in about 1945.

Keywords

Uranium Thorium 234U Thermal Ionization Mass Spectrometry Uranium Metal 

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Copyright information

© Springer-Verlag/Akadémiai Kiadó 2005

Authors and Affiliations

  • G. Hall
    • 1
  1. 1.Savannah River Technology Center, Nonproliferation Technology Section

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