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Advanced Detection Techniques Enhance Nuclear Material Analysis

Researchers at the Department of Energy’s Oak Ridge National Laboratory (ORNL) have achieved a significant milestone by successfully combining two analytical techniques to detect both fluorine and various isotopes of uranium simultaneously within a single particle. This dual detection capability is critical, as fluorine plays a vital role in converting uranium into forms that can be enriched, which is essential for both nuclear fuel production and nuclear weapon development.

The results of this innovative work have been published in the Journal of the American Chemical Society, showcasing advancements in the speed and accuracy of characterizing the chemical and isotopic properties of individual particles. Isotopes, which are variations of a chemical element with the same number of protons but different neutron counts, are crucial not only for understanding various chemical processes but also for dating materials.

According to Benjamin Manard, the lead researcher at ORNL, “Determining isotopic ratios on single particles has traditionally been a time-consuming process. Our advancements allow for rapid analysis, facilitating the identification of fluorine and uranium isotopes effectively.” The research team successfully analyzed 40 particles, each roughly equivalent in size to a red blood cell, in under five minutes.

The first method employed is known as laser-induced breakdown spectroscopy (LIBS), which excels at detecting fluorine with high sensitivity. “LIBS vaporizes the sample, such as uranyl fluoride particles, creating a plasma cloud of excited ions, from which we can monitor emitted light to identify elements,” explained Hunter Andrews, who led the LIBS component of the study. This process is likened to fireworks, where different elements emit distinct colors or wavelengths that can be measured.

Concurrently, helium gas conveys these plasma atoms into a mass spectrometer, where the second method—laser ablation multicollector inductively coupled plasma mass spectrometry (ICP-MS)—is applied. This approach uses radio-frequency energy to heat the plasma to extreme temperatures, reaching up to 8,000 kelvin, surpassing the heat of the sun.

“LIBS reveals the presence and quantity of fluorine, while ICP-MS identifies all uranium isotopes present in a particle,” Manard said. This integrated setup offers a comprehensive solution for simultaneously measuring both elements.

Identifying uranyl fluoride, a compound containing uranium, oxygen, and fluorine, is particularly significant from a nuclear nonproliferation perspective. Brian Ticknor, an ORNL co-author, noted that understanding the ratio of fluorine to uranium provides insights into the origin of the particle and the processes that led to its formation. He also highlighted that while these tools are primarily created for national security, they hold potential applications in diverse fields such as cutting-edge battery technology and environmental science investigating microplastics.

One challenge encountered in the past was integrating these two techniques due to fluorine’s strong tendency to form negative ions, making it less compatible with the ICP-MS method. “Typically, many elements can easily be converted into positive ions for mass spectrometry, but fluorine resists this change,” Ticknor explained. The research thus uniquely combines LIBS for fluorine and ICP-MS for uranium, a collaboration not previously realized in this manner.

Manard devised experiments for a multidisciplinary team at ORNL’s Ultra-trace Forensic Science Center, where sophisticated techniques for characterizing nuclear materials are employed to enhance the understanding of fuel cycle processes. Collaboration among ORNL members, including Cole Hexel, Paula Cable-Dunlap, and others, was instrumental in preparing samples and calibrating equipment to ensure precise measurements.

Looking ahead, the team plans to explore further applications of their technique, particularly for other challenging compounds linked to nuclear processes, such as uranium chloride, which could benefit from the established methods given its similar properties to fluorine.

“The implications of this dual analysis extend beyond nuclear nonproliferation, potentially illuminating the evolution of isotopes in various scientific domains,” Manard added. “We aim to push the limits of our techniques to analyze thousands of particles within a 24-hour timeframe while continuing to explore the capacity for distinguishing among different uranium compounds.”

More information:
Benjamin T. Manard et al, Uranium Single Particle Analysis for Simultaneous Fluorine and Uranium Isotopic Determinations via Laser-Induced Breakdown Spectroscopy/Laser Ablation–Multicollector–Inductively Coupled Plasma–Mass Spectrometry, Journal of the American Chemical Society (2024). DOI: 10.1021/jacs.4c03965

Source
phys.org