At Los Alamos National Laboratory, nuclear forensic scientists analyze samples of radioactive material to better understand nuclear crimes, such as the detonation of a nuclear device, the proliferation of nuclear material, or changes to a nuclear facility that go beyond what was previously disclosed in treaties.
Los Alamos scientists work continually to enhance nuclear forensics capabilities. Here are three Laboratory projects that were developed to help researchers analyze more types of samples more quickly and accurately. Each of these projects is funded through Los Alamos’ highly competitive Laboratory Directed Research and Development program.
Nuclear geology
In 2023, a team led by scientists Ann Junghans and Vlad Henzl developed a new sample collection technology—a coating that solidifies around a sample to preserve the chronological order of isotopes produced in a facility.
“You can imagine this like geology, where you have different defined layers of sediment that you can ideally trace to a certain period of time,” Junghans explains. “The idea was to preserve the layer structure—meaning the oldest material that was deposited first is at the bottom of the sample and the newest is on top.”
When applied to surfaces and heated with a handheld ultraviolet (UV) lamp, the polymer coating solidifies, trapping any heavy metals and other contaminants. Because sampled substances are encased in the polymer, they are not dangerous to handle.
In its original state as a liquid, the coating can be applied to cracks and crevices that are difficult to clean and sample. “We were able to almost completely retrieve the material and keep the layer structure intact,” says Junghans of an early experiment with the coating.
“This is compared to the traditional swipes, which do not have the resolution to see what is the first layer or second layer or third layer and can take several months to analyze,” adds Henzl, noting that the sample analysis took about 10 minutes.
In the future, this technology will enable facility inspectors to take more samples at a facility and thus develop a better understanding of what’s happening inside it. For example, explains scientist Rollin Lakis, “if a nation goes from producing low-enrichment uranium to high-enrichment uranium, there would be trace contaminants in its facilities that show that evolution to a possible weapons-relevant program. This product could see if that nation, in between making agreed upon concentrations of uranium in the context of a domestic fuel program, made high-enriched uranium for a clandestine weapons program and then tried to clean it up.”
Accelerating nuclear forensics
In October 2023, another Los Alamos team began working to decrease the time necessary to chemically separate elements within a sample. The isotopic composition and concentration of elements are pieces of evidence that reveal information about a sample, such as where the sample came from, when it was created, and what its intended use might be. That collective information is called “the provenance” of a sample. The provenance can give authorities actionable data, allowing them to prosecute potential nuclear crimes or trace producers and users.
“To make a claim based on a sample, we have to do a lot of chemistry and destructive analyses to extract very small and low-level (containing tens of thousands of atoms) concentrations of elements,” says scientist John Engel. “Current methods require multiple chemists working at multiple fume hoods for weeks.”
That’s why Engel and fellow scientist Jo Denton are trying to speed up the process—from one month to one week. Engel’s initial research developed a method for separating neptunium, americium, and plutonium from uranium samples. Now, he and Denton are working to add thorium and protactinium to that list.
To separate specific elements from a uranium sample, Engel and Denton use stacked column chromatography, in which a solid sample is dissolved in acid. The resulting fluid is placed into a series of vertically stacked columns containing different resins that bind certain elements. “In the first column, we have a resin that we know attracts neptunium and plutonium, and we’re hoping to show protactinium and thorium as well,” Engel says. “Then the rest drips through and americium sticks in the next column, and uranium continues through.” Users are then left with individual “cuts” of each purified element.
Fully separating the elements from each column requires further steps, but “the results can then be used as a screen of the data to get the ultimate level of precision through the established ways,” Engel explains. “With this information, we can make better decisions faster.”
Plutonium fingerprints
Scientist Kim Hinrichs is leading a project that focuses on low-level plutonium post-detonation samples—samples that could indicate whether a nuclear detonation has taken place.
Hinrichs collects plutonium samples from air filters onboard Constant Phoenix, a WC-135 aircraft that’s flown above potentially contaminated areas. Because only very small amounts of plutonium are collected in these filters, Hinrichs uses mass spectrometry—a process where atoms are separated by weight—to analyze them. Currently, this method works for all isotopes of plutonium except plutonium-238. That’s because if a sample contains naturally occuring and often abundant uranium-238, the measurements for plutonium-238 become skewed.
Hinrichs hopes to get accurate readings for plutonium-238 by developing a way to remove some uranium-238 from samples and also mathematically correct for uranium-238’s natural presence. With an accurate reading of all plutonium isotopes, analysts will be able to assess a sample more exactly and with higher confidence. This is important because different isotopes of plutonium are used for different applications—from nuclear weapons to heat sources for spacecraft.
“Essentially, you’re measuring an isotopic fingerprint for plutonium, and that fingerprint, that unique distribution of isotopes, tells you something about what the intended use or source of that plutonium might’ve been,” says program manager Stephen Lamont. “By being able to analyze more samples, we have a better chance of catching a bad actor and verifying whether a country is complying or out of compliance with its declared activities.” ★
Learn about NDAlpha, another new nuclear forensic technology, here.