In the latest edition of Science, an international team of chemists from the United States and Germany captures the fundamental chemistry of berkelium.
A false-color photomicrograph of the first isolated bulk (1.7 micrograms) sample of berkelium. Image credit: Oak Ridge National Laboratory.
Berkelium is a radioactive chemical element with symbol Bk and atomic number 97.
It is a member of the actinide group of elements, which are some of the heaviest, yet least understood chemical elements on Earth.
Berkelium is a silvery-white metal. It is attacked by oxygen, steam and acids, but not by alkalis.
The element was synthesized at and is named after the University of California, Berkeley.
It was discovered in 1949 by Stanley G. Thompson, Glenn T. Seaborg, Kenneth Street, Jr. and Albert Ghiorso, and was the fifth transuranium element synthesized.
In a series of experiments, the team led by Florida State University’s Prof. Thomas Albrecht-Schmitt and Colorado School of Mines’ Prof. Jenifer Braley made two distinct berkelium compounds: crystallized Bk(III)tris(dipicolinate) and Bk(III) borate.
The scientists also completed a series of measurements of the element to better understand its structural and chemical similarities to surrounding elements such as californium (Cf) and curium (Cm).
Through this process, they found that that berkelium was very similar to its periodic table neighbor californium in its structure, but chemically it had some significant differences.
“It’s electronically different than what people expected,” Prof. Albrecht-Schmitt said.
The crystals the team made developed such a positive nuclear charge that they started fragmenting shortly after they were assembled.
“We didn’t anticipate it. We just saw these tiny crystals exploding,” Prof. Albrecht-Schmitt said.
Berkelium has been mostly used to help scientists synthesize new elements such as element 117, tennessine, which was added to the table earlier this year. But little has been done to understand what the element alone can do and how it functions.
The U.S. Department of Energy gave the team only 13 milligrams of berkelium, roughly 1,000 times more than anyone has used for a major research study.
To run experiments though, they had to move quickly. The element reduces to half the amount in 320 days, at which point it is not stable enough for experiments.
“Because it is so radioactive, there is never much available. We had to capture the chemistry before nuclear decay destroyed the samples,” Prof. Albrecht-Schmitt said.
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Mark A. Silver et al. 2016. Characterization of berkelium(III) dipicolinate and borate compounds in solution and the solid state. Science 353 (6302); doi: 10.1126/science.aaf3762
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