Measured F(α,n) Yield from ²³⁴U in Uranium Hexafluoride

As new uranium enrichment plants are proposed and come online worldwide, interest in using neutron methods for uranium hexafluoride (UF₆) cylinder assay has been growing; however, large discrepancies exist in published F(α,n) yields from uranium isotopes. Uncertainties in these data are propagated through the analysis of every UF₆ measurement and have implications for safeguards conclusions drawn from them. In this paper, a value for the specific F(α,n) yield in UF₆ from ²³⁴U is calculated from measurements of 30B cylinders containing bulk UF₆ at the Rokkasho Enrichment Plant in Japan. The measurements were taken using the Uranium Cylinder Assay System. The yield was derived by combining the cylinder measurements with detailed Monte Carlo modeling, known isotopic composition, and inversion analysis. We calculated the ²³⁴U neutron emission rate in UF₆ to be (474 ± 21) n/s·g⁻¹ with a 68% confidence level. The results obtained in this study will help enable an important class of nondestructive assay instruments to be applied with greater confidence and accuracy.