Description
Lithium (Li) is a key material in the nuclear fusion field because it is a primary fuel for tritium production in the deuterium-tritium fuel cycle. Among two Li isotopes, $^{6}\text{Li}$ has been found to possess a higher cross-section than $^{7}\text{Li}$ for tritium breeding in the nuclear fusion power plant. However, the abundance of $^{6}\text{Li}$ in nature is only 7.53% while the abundance of $^{7}\text{Li}$ is 92.47%. Coupled with Li isotopes enrichment methods, a reliable technique for analyzing Li isotopes abundance is essential. In our work, a laser-produced vapor for laser-induced breakdown spectroscopy (LPV-LIBS) was developed for measuring Li isotope abundances of Li liquid samples. The Li liquid samples were prepared from $^{6}\text{Li}$-enriched and $^{7}\text{Li}$-enriched Li hydroxide. There are 21 samples with the $^{6}\text{Li}$ abundances ranging from 0.01% to 95%. The LPV-LIBS system was configured using a 20 Hz nanosecond Nd:YAG pulse laser having two output beams. The first beam at 532 nm of wavelength was focused in the liquid to vaporize the Li. The second beam at 1064 nm of wavelength was focused on the Li vapor to generate the laser-produced Li plasma. The plasma emission light was collected via a multimode fiber and an external lens system, then was detected by a spectrometer. Li 2s-2p transition line was observed in the plasma spectra. A distinct spectral redshift of the Li 2s-2p line was identified as the $^{6}\text{Li}$ abundance increased. The relationship between the $^{6}\text{Li}$ isotopes abundances in the liquid and the corresponding spectral shifts of the Li 2s-2p transition line was discussed. The error in determining $^{6}\text{Li}$ abundance achieved a precision of ±2% by the developed LPV-LIBS.