Oak Ridge radiochemist tweaks techniques to extract radioisotopes for research

Researchers at Oak Ridge National Laboratory are developing techniques to improve the purification of highly valued radioisotopes that are byproducts of californium-252 production. ORNL radiochemist Cristian A. Celis-Barros is leading the effort, with the goal of enhancing yields of very small amounts of berkelium-249, einsteinium-253 and -254, and fermium-257. These isotopes are valued for their applications in research, especially the search for new heavy elements.

Cf-252 for industry: ORNL is the only facility in the Western Hemisphere that produces Cf-252, a neutron-emitting radioisotope that has a number of applications. It is used in the startup of nuclear reactors and to assay fresh reactor fuel, as well as in applications related to oil well logging, national security, and other purposes. The Cf-252 that is produced at ORNL is made available to an industrial consortium that fabricates and distributes the finished, sealed sources to customers around the world.

The production of Cf-252 at ORNL is funded by the Department of Energy's Office of Isotope R&D and Production, which is also funding the work to improve the byproduct purification processes.

Studying the heaviest elements: According to ORNL, during Cf-252 production, "milligrams of berkelium-249; micrograms of einsteinium-253/254; and picograms of fermium-257" are generated. These "rare radioisotopes allow scientists to study the heaviest elements on the periodic table-and discover new elements," the lab said. "ORNL-produced Bk-249 was famously used in the discovery of superheavy element 117, tennessine. ORNL-produced radioisotopes were also used in the discoveries and confirmations of superheavy elements 114, flerovium; 115, moscovium; 116, livermorium; and 118, oganesson."

Improving chemical separation processes: Celis-Barros and his team have been working on improving chemical separation processes that were originally developed by now-retired ORNL researcher Miting Du about five years ago. Celis-Barros explained, "We're just trying to simplify and come up with processes that are more efficient and expose workers to less radiation."

Celis-Barros added a step to Du's process for purifying Bk-249, in which the berkelium is run through an extra chromatography column that retains the radioisotope while allowing various impurities to pass through, thereby increasing radiochemical purity and changing the color of the resulting solution from a "muddled yellowish solution to a pure solid crystalline green: visual evidence of its purity," according to ORNL. This revised Bk-249 purification process is currently undergoing additional tests before being implemented by ORNL.

For einsteinium, Celis-Barros made use of the same type of extra column that he used for Bk-249, but he also made other adjustments that optimized conditions for Es-253 and Es-254 separation from Cf-252. His efforts so far have improved the recovery rate of the Es-253 and Es-254 to 95 percent for each column run-substantially more than was possible with previous techniques.

The team used a different type of chromatography column for Fm-257 separation, one made with an alternate kind of extraction resin from the diglycolamide (DGA) resin that is typically used in separation/extraction techniques. According to Celis-Barros, the improved technique-which resulted in a chemical purity of about 99.93 percent-has made researchers, especially physicists, more interested in separating Es-253 and Es-254 from Fm-257.

Rock stars: In 2027, Celis-Barros and his team-who he describes as "rock stars"-plan to further improve the radioisotope separation techniques that they have developed. He says, "We're hoping to be even more efficient and recover more than we did, because we know now how to make it happen and how to prepare for it."

He adds that all of the radioisotope work that is taking place at ORNL is "definitely pushing the boundaries of chemistry. Not even all the textbooks are updated with all the stuff we can do. It's pretty entertaining and exciting."