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Physical Chemistry

Element 117 Created

Nuclear Chemistry: Elusive superheavy element fills out picture of periodic table's extremes

by Elizabeth K. Wilson and Jyllian Kemsley
April 12, 2010 | A version of this story appeared in Volume 88, Issue 15

Credit: Department of Energy/ORNL
RARE PRECURSOR Scientists used the radioactive 249Bk starting material, shown through protected glass in a chamber, to generate element 117.
Credit: Department of Energy/ORNL
RARE PRECURSOR Scientists used the radioactive 249Bk starting material, shown through protected glass in a chamber, to generate element 117.

Scientists report they have created the especially shifty superheavy element 117, a milestone for nuclear chemistry that now completes the seventh row of the periodic table.

The discovery, which will be published in an upcoming issue of Physical Review Letters, helps clarify the still-fuzzy picture of the behavior of extremely heavy elements. It also bolsters the case for the existence of an "island of stability," where a cluster of superheavy elements that have very long half-lives holds out to scientists the tantalizing prospect of doing superheavy-element chemistry.

Yuri Oganessian, director of the Flerov Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research, in Dubna, Russia, led the international team, which also included scientists from Lawrence Livermore National Laboratory (LLNL), Oak Ridge National Laboratory, Vanderbilt University, and the University of Nevada, Las Vegas.

With a particle accelerator at Dubna, the group repeatedly smashed calcium-48 into a target coated with the radioactive berkelium-249. In rare instances, the two elements fused to produce two isotopes of the new superheavy element, 293117 and 294117. They identified element 117 from its characteristic decay chains. Like its cousin elements 116 and 118—which have already been created—element 117 has isotopes with half-lives that are in keeping with theories of elements near the presumed island of stability, which has elements with 184 neutrons.

Element 117 was more difficult to create than 116 and 118 for a number of reasons, says team member and LLNL nuclear chemist Dawn Shaughnessy. Odd-numbered elements have more complex decay chains. In addition, the starting material 249Bk has a half-life of only a year, making it difficult to coordinate experiments, she says.

Walter D. Loveland, a nuclear chemistry professor at Oregon State University, called the creation of the periodic table's newest entry a "special event for all of science."

Andreas Türler, head of the Laboratory of Radiochemistry & Environmental Chemistry at the University of Bern, in Germany, tells C&EN that "the work is of the same quality as other recent experiments performed on heavy elements in Dubna."

Before element 117 can be named, the International Union of Pure & Applied Chemistry requires that the element's creation be replicated by an independent team.

Shaughnessy says she's not even considering possible name options because the confirmation process can be lengthy. "You could drive yourself crazy thinking about something that won't happen for 10 years," she says, laughing.



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