Measurements of235U/238U isotopic ratio in the photoproduct UF5 by multiphoton ionization and time-of-flight mass spectrometry

A MultiPhoton-Ionization Time-Of-Flight Mass Spectrometry (MPI/TOFMS) apparatus was developed for real-time measurement of the uranium isotopic ratio in nascent UF₅ formed by the 266 nm photolysis of effusive UF₆ ( < 300 K, 1.3 × 10^–4 Pa). The UF₅ was selectively and efficiently multiphoton ionized by 532 nm radiation at appreciably low fluences ( < 10 J/cm²). The main ions observed, U⁺ and U²⁺, were subsequently analyzed with a TOFMS with mass resolution of 1190 to separate²³⁵U ⁿ⁺ and²³⁸U ⁿ⁺ completely. The isotopic ratio measurements showed good precision resulting from the excellent agreement which was observed between the isotopic ratios in UF₅ products and those in a parent UF₆ sample. These results suggested that the MPI/TOFMS method can be applied to the real-time analysis of separation factors in the molecular laser isotope separation of uranium by ionization of UF₅ following the infrared photodissociation of UF₆.