Temperature effect on laser-induced breakdown spectroscopy spectra of molten and solid salts

Laser-induced breakdown spectroscopy (LIBS) has been investigated as a potential analytical tool to improve operations and safeguards for electrorefiners, such as those used in processing spent nuclear fuel. This study set out to better understand the effect of sample temperature and physical state on LIBS spectra of molten and solid salts by building calibration curves of cerium and assessing self-absorption, plasma temperature, electron density, and local thermal equilibrium (LTE). Samples were composed of a LiCl–KCl eutectic salt, an internal standard of MnCl₂, and varying concentrations of CeCl₃ (0.1, 0.3, 0.5, 0.8, and 1.0 wt.% Ce) under different temperatures (773, 723, 673, 623, and 573 K). Analysis of salts in their molten form is preferred as plasma plumes from molten samples experienced less self-absorption, less variability in plasma temperature, and higher clearance of the minimum electron density required for local thermal equilibrium. These differences are attributed to plasma dynamics as a result of phase changes. Spectral reproducibility was also better in the molten state due to sample homogeneity. - Highlights: • Effect of temperature on LIBS spectra and conditions is presented for molten salt samples. • Signal intensity varied with physical state in the order transition > solid > molten state. • Temperature changes within the molten state also affected signal intensity. • For the given experimental parameters, self-absorption is least for the molten state. • Samples in the molten state gave the most homogeneous LIBS spectra