Neutron methods for monitoring the blending of enriched UF6 gas

Blending a highly enriched UF₆ gas stream with low-enrichment material reduces the excess supply of highly enriched uranium that must be closely controlled for nonproliferation of nuclear weapons. Computer simulations and feasibility experiments show that inducing fission in ²³⁵U provides means for monitoring the blending process. Detecting delayed fission neutrons or gamma rays after fission products drift downstream in the gas gives a measure of ²³⁵ U content and flow velocity. At very low UF₆ gas pressures (5 mm Hg) where the downstream signal is too weak for use, an alternative technique based on attenuation of thermal neutrons passing through the UF₆ gives a measure of ²³⁵U content