International nuclear safeguards verification relies on a precise count of isotope particles collected on swipes during International Atomic Energy Agency inspections of nuclear facilities and isolated through a series of lengthy chemical separations that can take about 30 days to complete. On October 15, Oak Ridge National Laboratory—a member of the IAEA’s Network of Analytical Laboratories (NWAL)—announced that analytical chemists at the site have developed a faster way to measure isotopic ratios of uranium and plutonium collected on swipes, which could help IAEA analysts detect the presence of undeclared nuclear activities or material.
Proof of concept: ORNL’s Benjamin Manard led a proof-of-concept study, which demonstrated that a commercially available pen-sized microextraction probe could be coupled to a mass spectrometer. The resulting paper, “Direct Uranium Isotopic Analysis of Swipe Surfaces by Microextraction-ICP-MS,” was published in the August 17 issue of Analytical Chemistry and featured on the journal’s cover. The Department of Energy’s National Nuclear Security Administration supported the project.
“It truly is an integrated system,” Manard said. “With just a click of a button, you’re going from a solid sample on a swipe to an isotopic measurement.” By contrast, traditional analysis has required processing samples in a furnace and through a lengthy series of chemical separations that could typically take up to 30 days, according to ORNL.
Methods and results: To take a measurement, an analyst places a swipe on the extraction stage, selects a region of interest measuring about 8 mm2, and presses a button to start the process. The microextraction probe is lowered onto the swipe, where it seals the swipe to the surface of the stage and delivers a nitric acid solvent to dissolve any actinides. Then the probe functions like a wet vacuum to carry the solution into a mass spectrometer that subjects the extracted material to a hot plasma and measures the mass-to-charge ratios of the ions generated from the sample.
The team was able to detect as little as 50 picograms of uranium—80 million times lighter than a grain of sand—in nuclear reference materials and measure the ratios of major and minor isotopes of uranium. In a subsequent study, the researchers applied the same technique to the analysis of plutonium.
ORNL’s system extracts a solid from a swipe, ionizes it with a plasma torch, and measures the mass-to-charge ratio of its ions with a mass spectrometer. (Animation: Jaimee Janiga and Michelle Lehman/ORNL, DOE)
Applications and refinement: Paper coauthor Shalina Metzger has proposed adding a chromatography column to the system between the microextraction probe and the mass spectrometer, according to ORNL. As actinide-containing solutions flow through the chromatography column, plutonium would be captured for later measurement while uranium would flow through to the mass spectrometer, improving elemental sensitivity and identification.
The researchers plan to experiment with changes to the solvent and the microextraction probe head to avoid observed degradation of the probe head. “We’re also using ORNL’s unique 3D-printing facilities to fabricate components with polymers that are more resistant to the extraction solvent,” Manard said.
Manard and his coauthors work in ORNL’s Ultra-Trace Forensic Science Center, a service center and research facility providing expertise and state-of-the-art inorganic mass spectrometry instrumentation. While the research team focused on nuclear safeguards and verification applications, the new technique could be used in other applications requiring elemental and isotopic analysis of solid samples, according to ORNL.