Uranium enrichment measurements using tunable laser spectroscopy coupled with fiber-optic laser-induced breakdown spectroscopy

Tunable laser absorption spectroscopy (LAS) and laser induced fluorescence (LIF) were combined with fiber-optic laser-induced breakdown spectroscopy (FOLIBS) to characterize 238U and 235U isotopes from a natural uranium (NU) sample. Time-resolved absorption spectroscopy (TRAS) and two-dimensional fluorescence spectroscopy (2D-FS), derived from LAS and LIF respectively, were utilized to visualize uranium isotope shifts. These techniques clearly differentiated the isotopic shift of the U I 394.382 nm transition (approximate to 8.7 GHz) and identified partially resolved hyperfine structures of 235U. Isotope ratio analysis for NU was conducted under 10 torr and 30 torr N2 background gas, and TRAS measurement showed good agreement. However, strong reabsorption in 2D-FS hindered accurate isotope ratio measurements. These rapid, accurate, non-contact laser spectroscopic techniques are promising for in situ measurement of uranium isotopes in hazardous environments, applicable to nuclear energy, safeguards, and forensics.