A ribbon-cutting ceremony was held August 17 to formally open the Argonne TRACER Center (Trace Radioisotope Analysis Center) at the U.S. Department of Energy’s (DOE) Argonne National Laboratory. The TRACER Center provides a new, permanent home for the nation’s only laser-based krypton atom-counting machine.
The center employs a novel technique called Atom Trap Trace Analysis (ATTA) that captures and counts isotopes of the rare element krypton (Kr) to determine the age of ice and groundwater. One of only a few such devices in the world, it provides valuable information about the dynamics, flow rates, and direction of water in aquifers, particularly those vital to arid regions.
“The TRACER Center is the culmination of 15 years of work that has been supported by both DOE Nuclear Physics and the laboratory,” said John Arrington, associate director of Argonne’s Physics division. “With that support, we are now able to provide a greatly enhanced analysis capability and greater field portability for users, and support a long-term vision for expanding to different isotopes.”
Where the initial ATTA system could analyze about 100 samples a year, the TRACER Center is equipped with two ATTA machines, a state-of-the-art high-throughput system and a dedicated research and development beamline. This combination will allow the research team to more than triple the number of samples analyzed, while simultaneously focusing on research and development for future improvements.
Current work focuses on the isotopes 81Kr, used to date ice or water with an age range of approximately 20,000 to 2 million years, and 85Kr, which dates on the 5- to 50-year scale. New R&D will optimize the process and help in the design of additional instrumentation to analyze different isotopes like 39Argon that has an intermediate age range ideal for young groundwater and ocean circulation studies.
Another key enhancement to the project has been the portable gear that allows users to obtain their own field samples, a process that once meant collecting tens of thousands of liters of water. Today, that number has been reduced to roughly one hundred liters and can be collected by facility users outfitted with compact gas extraction systems. Users then send the extracted samples to Argonne for purification analysis.
“We’re becoming a more customer-oriented operation by making the technique available and teaching people how it can address their needs,” said Peter Mueller, the TRACER Center’s principal investigator. “We now have all the technical capabilities our customers need to meet their research objectives.”
“… we are now able to provide increased analysis capability and greater field portability for users, and support a long-term vision for expanding to different isotopes.” John Arrington, associate director of Argonne’s Physics division
Detecting 81Kr is extremely challenging. Where krypton accounts for one in every million atoms in the atmosphere, less than one in every trillion of those is an atom of 81Kr.
To determine the age of an ice or water sample, krypton gas extracted from the water sample is injected into the ATTA beamline. Lasers are used to cool and trap atoms of a selected isotope at the end of the beamline, where the trapped atoms scatter laser light into a camera, providing a means by which to count them.
Once the sample measurement is complete, a calibrated reference gas of pure krypton containing the natural atmospheric abundance is injected into the system and measured in the same manner for comparison.
Radioactive isotopes are characterized by their half-life, or the time it takes for half of the atoms to decay into a different element. In the case of 81Kr, half of the atoms will decay into the element bromine after 230,000 years.
If the number of 81Kr atoms in the sample is only half of that in the reference gas, then an average of 230,000 years have passed since the water or ice has been in contact with the atmosphere.
So far, ATTA has dated samples from diverse and extreme geographies from wetlands and deserts to glacial ice. Its users have included the U.S. Geological Survey, Sandia National Laboratory, the University of Chicago, and Ben-Gurion University of the Negev in Israel.
Reika Yokochi studies subsurface fluids and the information they carry, including that of paleoclimates. A research associate professor in the University of Chicago’s Department of the Geophysical Sciences, she has worked with the ATTA team since 2012, measuring samples extracted from aquifers in Florida and Israel, as well as hydrothermal systems in Yellowstone National Park.
“It’s exciting that they can continue R&D in parallel with sample analyses, since slightly higher precision will dramatically increase the use of this tracer for paleoclimate research, and smaller sample sizes will broaden the field of application,” said Yokochi.
Funding for the ATTA technique and its initial facility was provided by the Office of Nuclear Physics within the Department of Energy’s Office of Science and through Argonne’s Laboratory Directed Research and Development program. Construction of the Argonne TRACER Center was supported through program development funds.
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