Lanzhou University Breakthrough in High-Precision Lithium Isotope Detection
A research team at Lanzhou University has achieved a landmark breakthrough in high-precision lithium isotope detection, successfully resolving the long-elusive lithium doublet structure and isotope shift peaks using laser-induced breakdown spectroscopy (LIBS). The advancement, published in the Journal of the American Chemical Society (JACS), opens transformative possibilities for real-time monitoring in nuclear fusion and fission reactors.
According to Science and Technology Daily, the team — led by Professor Liu Zuoye at the Rare Isotope Frontier Science Center and School of Nuclear Science and Technology — developed a novel technique called “Time-Space Medium Synergistic Modulation LIBS” (TSMM-LIBS). This method coordinates three dimensions — time, space, and medium environment — to actively regulate the laser-induced high-temperature plasma core, fundamentally suppressing the self-absorption effects that have long hindered lithium isotope analysis.
The Challenge of Lithium Isotope Detection
Lithium has two stable isotopes: ⁶Li (approximately 7.5% natural abundance) and ⁷Li (approximately 92.5% natural abundance). Both are critical for nuclear technology. ⁶Li is essential for tritium breeding in nuclear fusion reactors — when bombarded with neutrons, it produces tritium and helium, the primary fuel pathway for future fusion power plants. ⁷Li is used as a coolant additive in pressurized water reactors to control pH and reduce corrosion.
Traditional isotope analysis relies on mass spectrometry techniques such as Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Thermal Ionization Mass Spectrometry (TIMS). However, as detailed by the China Nuclear Technology Network (CCNTA), these methods face significant challenges in nuclear industry settings: high radioactive contamination risk, complex sample matrices requiring difficult separation and purification, radiation exposure to personnel, and regulatory constraints under nuclear safeguards that restrict sampling and off-site analysis.
LIBS technology offers distinct advantages for nuclear applications — remote detection capability, rapid response, real-time monitoring, and adaptability to high-radiation environments. Yet it faced a critical bottleneck: the lithium characteristic line at 670.776 nm is highly susceptible to self-absorption effects that cause spectral distortion, while the isotope shift between ⁶Li and ⁷Li is only approximately 15 picometers (pm), easily masked by plasma broadening and self-absorption.
Technical Breakthrough
The TSMM-LIBS method developed by Professor Liu’s team tackles this challenge through an innovative multi-dimensional approach. The team also introduced several key innovations: the first-ever definition of a “Self-Reversal Index” (SRI) for quantitative characterization of spectral line distortion, a wing-side recovery algorithm combining the Beer-Lambert law to extract isotope information from distorted signals, and a matrix dilution strategy to further suppress self-absorption effects.
As Xinhua News Agency reported, the team achieved the simultaneous observation of three characteristic peaks of lithium isotopes: 670.776 nm (⁷Li D₂ line), 670.791 nm (⁷Li D₁ and ⁶Li D₂ line), and 670.807 nm (⁶Li D₁ line). Through synergistic modulation and matrix dilution, the spectral full width at half maximum (FWHM) was compressed to 25.65 pm, with Stark broadening reduced to 3.87 pm, achieving sub-Doppler spectral resolution.
In quantitative analysis, the team established a self-absorption-corrected effective concentration model. Cross-validation results showed a root mean square error (RMSE) as low as 0.041 and a performance-to-deviation ratio (PDR) of 6.561 — far exceeding the industry excellent standard of 2.0.
Implications for Nuclear Energy
“This technological breakthrough provides a transformative technical pathway for high-precision in-situ detection of isotopes in tritium breeding materials for nuclear fusion energy systems and coolants for nuclear fission reactors,” Professor Liu Zuoye said, as reported by Science and Technology Daily.
The research has direct applications across multiple nuclear domains. For fusion energy, real-time monitoring of tritium breeding materials such as Li₂TiO₃ ceramics is critical for the fuel cycle of reactors like ITER and China’s own China Fusion Engineering Test Reactor (CFETR). This technology could enable continuous, non-contact monitoring of ⁶Li depletion and tritium production. For fission reactors, the ability to remotely and rapidly analyze lithium isotopes in reactor coolants could improve safety monitoring and fuel cycle management.
China is actively developing both nuclear fission and fusion energy. The country has the world’s largest在建 nuclear power program, is a key participant in the ITER project, and is developing CFETR. The Chinese government has identified nuclear fusion energy as a future industry priority. This breakthrough provides a crucial enabling technology for the fuel cycle of future fusion reactors.
Publication and Support
The research, titled “Time-Space-Medium Collaboratively Modulated LIBS Combined with Matrix Dilution: From Self-Absorption to Isotope Discrimination of Lithium,” was published in JACS, one of the world’s most prestigious chemistry journals. The first author is doctoral candidate Lai Zhihang, a joint engineering master’s-doctoral student at Lanzhou University’s School of Nuclear Science and Technology. Professor Liu Zuoye is the sole corresponding author.
The work was supported by the National Natural Science Foundation of China and the CNNC (China National Nuclear Corporation) Leading Innovation Project.
Looking Ahead
The TSMM-LIBS method represents a fundamental advancement in laser spectroscopy, overcoming a limitation that has constrained LIBS isotope analysis for years. The sub-Doppler spectral resolution achieved approaches the emission quality of hollow cathode lamps — remarkable for a laser-induced plasma source.
Outstanding questions remain regarding the Technology Readiness Level of TSMM-LIBS and how close it is to deployment in actual nuclear facilities. Researchers will also explore whether this method can be extended to other isotopes beyond lithium, such as uranium and plutonium, and how its detection sensitivity performs at very low isotope concentrations. The cost and complexity comparison with traditional mass spectrometry methods will also be a key factor in determining the technology’s path to commercial adoption.
Reporting based on sources from Science and Technology Daily, China Nuclear Technology Network (CCNTA), Xinhua News Agency, and People Daily.