Effect of liquid-sheet jet flow velocity on lithium detection sensitivity in aqueous solutions via laser-induced breakdown spectroscopy

Abstract

To ensure the safe operation of nuclear facilities, real-time, on-site, and highly sensitive monitoring of elemental concentrations in nuclear-related liquids is crucial. Laser-Induced Breakdown Spectroscopy (LIBS) demonstrates attractive potential for on-site, real-time analysis in nuclear applications. However, challenges such as liquid splashing, surface fluctuations, and plasma quenching reduce the LIBS spectral intensity and stability, thereby lowering its detection sensitivity. The liquid jet is a straightforward method to improve the LIBS detection capability. Compared to traditional liquid jets, liquid-sheet jets can further enhance the LIBS detection sensitivity. In this work, we propose a novel approach of liquid-sheet jet LIBS to enhance detection sensitivity by optimizing the flow velocity. The effect of liquid-sheet flow velocity on the sensitivity of LIBS for detecting lithium in simulated nuclear reactor coolant was investigated. A mechanistic analysis was conducted to examine how variations in flow velocity influence plasma lifetime, electron density, and excitation temperature. The results showed that these changes improved the signal-to-noise ratio (SNR) and enhanced detection sensitivity. At an optimal flow velocity of 12.47 m s⁻¹ when the flat nozzle has a width of 2.15 mm and a thickness of 0.43 mm, the method achieved a limit of detection (LOD) of 0.15 mg L⁻¹ for lithium, fully meeting the requirements for monitoring lithium concentrations in pressurized water reactor coolants. It is indicated that optimizing the flow velocity of the liquid-sheet jet significantly enhances plasma signal intensity. This approach does not require sampling and pre-preparation, while offering a simple and rapid detection process. The results highlight the potential of LIBS for monitoring in the nuclear industry and suggest that further optimization could extend its applicability to other fields.