The detection of uranium isotopes in a timely manner contributes to the security of radioactive materials

The detection of uranium isotopes in a timely manner contributes to the security of radioactive materials

Oak Ridge National Laboratory analytical chemists have developed a rapid method for determining the isotopic ratios of uranium and plutonium collected during environmental swipes at the Department of Energy's Oak Ridge National Laboratory. This method may be used to assist analysts at the International Atomic Energy Agency in detecting the presence of undeclared nuclear activities or material, according to the agency.

In the words of ORNL's Benjamin Manard, "This method is based on a commercial microextraction probe that samples solids directly before extracting analytes from the surface and into a flowing solution." This sampling mechanism was found to be capable of extracting actinide material (such as uranium and plutonium) from environmental swipes, which he oversaw during the proof-of-concept study. The article was featured on the front cover of the journal Analytical Chemistry, among other places.

Using this advancement, the International Atomic Energy Agency's Network of Analytical Laboratories, or NWAL, which includes ORNL, could be able to analyze samples collected from facilities around the world more quickly and efficiently. "If the microextraction method can be refined to achieve sufficient precision and accuracy," says Brian Ticknor, DOE NWAL coordinator and co-author, "it may be possible to increase sample throughput while simultaneously decreasing turnaround time."

This product's pen-sized microextraction probe uses a "wet vacuum" to mobilize material from a swipe surface, similar to that of the Advion Plate Express product. As part of the experiment, Manard's team connects the probe to an instrument that subjected the extracted material to plasma — a hot, ionized gas hotter than the surface of the sun — and measured the mass-charge ratios of the ions generated from the sample.

In the words of Manard, "it is truly a unified system." An analyst swipes across the extraction stage, selects a region of interest, and then presses a button to begin the process of extracting the information. An acid solvent is injected into the swipe through the microextraction probe, which is then sealed to the stage surface and lowered onto the swipe to dissolve any actinides present in the swipe. After that, the actinide solution is injected into a mass spectrometer for further examination. As he explained, "you can transition from a solid sample to an isotopic measurement with a single click of the button."

Ornithological Research Laboratory (ORNL) co-author Kayron Rogers used this innovative approach to solids analysis to create an array of swipe samples containing varying amounts of reference standards. They were able to detect uranium as small as 50 picograms, which is equivalent to 80 million times the weight of a grain of sand in terms of mass. Furthermore, the researchers were able to determine the ratios of major and minor isotopes of elements in nuclear reference materials with high precision and accuracy thanks to the use of advanced techniques. In a subsequent study, they applied the technique to the analysis of plutonium, which was successful.

According to Manard, "the advantages of this methodology may extend beyond the analysis of nuclear materials to a wide variety of applications that require direct elemental analysis."

Traditionally, analysts would use a furnace to inspect ash samples before subjecting them to acid digestion and lengthy chemical extractions. The entire process, from ashing to analysis, can take up to 30 days on average. "The goal of this project was to reduce the amount of time spent in the initial stages of ashing and dissolution," Manard explained. "If we could sample the swipe directly, we would be able to avoid the time-consuming process of attempting to convert it to a liquid," says the researcher.

The researchers are based at the Oak Ridge National Laboratory's Ultra-Trace Forensic Science Center, which is a service and research facility that specializes in inorganic mass spectrometry and other forensic techniques. This project brings together ideas and technologies developed at Oak Ridge National Laboratory that have the potential to revolutionize environmental sampling methodology, according to co-author Cole Hexel, who directs the laboratory's Chemical and Isotopic Mass Spectrometry Group.

The researchers are looking forward to conducting experiments over the next two years to evaluate the methodology's adaptability. They hope to complete the experiments by the end of the year.

Using Shalina Metzger's novel approach, actinide-containing solutions are allowed to flow through connective tubing sandwiched between a chromatography column and the microextraction probe and then analyzed by the mass spectrometer. While the column would allow for the flow of uranium, it would also retain plutonium for subsequent elution and analysis. A more sensitive and accurate identification of elements would be achieved through this method.

When the researchers carried out their experiments, they discovered that nitric acid degraded the microextraction probe head. It is planned to conduct additional research to optimize the solvent conditions for extracting actinides in their various chemical forms. "We're also taking advantage of ORNL's unique 3D printing capabilities to fabricate components made of polymers that are more resistant to the extraction solvent," Manard explained further.

Researchers at Oak Ridge National Laboratory (ORNL) hope to eventually develop the capability to differentiate individual analytes collected during a swipe in order to provide a more comprehensive picture of the operations of a facility under inspection. As a revolutionary approach toward that goal, their method of combing microextraction and mass spectrometry shows promise as a revolutionary approach toward that goal. Manard's team is optimistic that the research that will take place in the coming years will bear fruit and allow him to achieve his goal.

The paper is titled "Direct Uranium Isotopic Analysis of Swipe Surfaces by Microextraction-ICP-MS," and it is available online.