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

Abstract

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 (≈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.