Application of the 226Ra-230Th-234U and 227Ac-231Pa-235U radiochronometers to UF6 cylinders

Uranium-series radiometric dating was performed on two well-pedigreed UF6 cylinder samples containing highly enriched uranium that were in use at the Portsmouth Gaseous Diffusion Plant between the mid-1970s and mid-1980s. Daughter-parent (i.e. Pa-231-U-235, Th-230-U-234) radiometric ages determined on solid heel materials (e.g. UO2F2, UF4) recovered from the emptied cylinders are unrealistically old due to the preferential sequestration of progeny isotopes relative to uranium within the solid heels. However, limited elemental fractionation amongst the progeny isotopes themselves in the heel material allowed for realistic age constraints on the fill dates of the UF6 cylinders to be extracted from the granddaughter-daughter systems (i.e. Ra-226-Th-230, Ac-227-Pa-231).