Ratio of 1275 and 18₆-keV Gamma Ray Count Rates for Age Determination of Material in Uranium Hexafluoride Cylinders

In this work, a method for using ratios of passive gamma ray measurements to determine the time since the filling of UF₆ cylinders was explored. This method uses the 186 keV gamma ray emitted by ²³⁵U and the 1,275 keV gamma ray that results from interactions of alpha particles in fluorine. Studies were made using MCNP models of both 30B cylinders and smaller 5A cylinders. Results indicate that for enrichments at or above that of natural uranium, this approach may provide a method for determining age up to 10 years or identifying whether the age is greater than 10 years, even if the uranium enrichment is unknown. The calculated results show the same behavior as the results of a recent measurement campaign, indicating the possibility of using this method for real-world cylinders.