After a year of fastidious planning, a microscopic sample of the ultra-rare radioactive element berkelium arrived at a Berkeley Lab. With just 48 hours to experiment before it would become unusable, a group of nearly 20 researchers focused intently on creating a brand-new molecule.
Using a chemical glove box, a polycarbonate glass box with protruding gloves that shields substances from oxygen and moisture, scientists combined the berkelium metal with an organic molecule containing only carbon and hydrogen to create a chemical reaction.
Post-doc researcher Dominic Russo said he had previously performed similar experiments that had not gone quite according to plan. Those solutions, he said, turned a reddish color, which signaled failure. The latest experiment with berkelium offered something entirely new to him as he watched the solution turn a dark violet — a chemist’s version of watching “The Wizard of Oz” turn from black and white to technicolor for the first time.
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“That’s a different color — I don’t know what that is,” Russo said, recalling the day of the experiment. “The color was very promising, the solubility was very promising. … Seeing the picture a few hours after (via an X-ray diffraction spectrometer image), that was sort of the eureka moment.”
They’d done it.
Russo, researcher Stefan Minasian, and 17 other scientists at Lawrence Berkeley National Laboratory had created berkelocene, a new molecule that usurps theorists’ expectations about how carbon bonds with heavy-metal elements. In the future, berkelocene may help humanity safely dispose of nuclear waste, according to a study published in the academic journal Science in February.
“This is testing what we’re capable of, so it’s exploring everything to do with Mother Nature,” researcher Polly Arnold said. “We’re part of a really large number of people around the world who are trying to safeguard all of our civil nuclear waste and all of the isotopes that we have.”
Berkelium was discovered by acclaimed UC Berkeley chemist and pioneering nuclear medicine pioneer Glenn Seaborg in 1949 and remains one of the rarest synthetic elements in the world. The element and its molecular counterpart are both named after the city of Berkeley. Since 1967, just over one gram of berkelium has been produced in the United States — the majority of which comes from Oak Ridge National Laboratory in Tennessee. Berkeley Lab’s experiment acquired just 0.3 micrograms for its experiment. Adding to the challenging nature of the element, berkelium is highly air sensitive and radioactive, making it extremely onerous to work with.
“People have been able to do air-sensitive chemistry and have been able to do radioactive work with radioactive elements for a long time,” Minasian said, “but marrying those two fields has been a lot harder.”
After a sample of the resulting berkelocene had been synthesized into a crystal, researchers deployed an X-ray diffraction spectrometer to reveal the team had, in fact, discovered a new molecule. The new molecular structure is, in the nomenclature of researchers, a “sandwich.” In this formation, a berkelium atom, serving as the filling, lays in between two 8-membered carbon rings — the “bread” — and resembles an atomic foot-long sub.
“It has this very symmetric geometry, and it’s the first time that that’s been observed,” Minasian said. “Really high symmetry structures are great for chemists. Because when we are trying to understand why an element decides to organize itself in a particular way and you see symmetry, it helps you then develop an understanding.”
Interest in radioactive carbon bonds like these has persisted in the world of chemistry since they were first investigated for applications in the Manhattan Project, the United States’ top-secret research project to create the atomic bomb during World War II. While past “sandwiches” have been used to more efficiently combust the hydrocarbons in gasoline, the discovery of berkelocene may eventually aid scientists as they seek a solution to safely dispose of radioactive waste, Arnold said.
So far, world leaders’ best bet to rid their countries of radiation has been to push nuclear waste deep underground where, hopefully, no one can access it now or, for the most dangerous waste products, in the next million years. While eliminating nuclear waste won’t be achieved by “berkelium sandwiches,” Arnold said, Berkeley Lab’s breakthrough may provide a scientific foundation that advances humanity toward that end goal.
“We showed that its properties weren’t what you would predict from just looking at its position in the periodic table,” Arnold said. “One day, we won’t have to do these risky reactions. One day, theory will be able to predict things, and they might be able to predict the long-term storage, where we can’t do it so easily.”