September 6, 2000

Berkeley Lab Science Beat

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BERKELEY, CA — An international collaboration of radiochemists has determined the volatility of bohrium, element 107 -- the heaviest element yet whose chemistry has been successfully investigated. The researchers, led by Heinz Gaggeler of the University of Bern and the Paul Scherrer Institute (PSI) in Villigen, Switzerland, publish their work in the 7 September 2000 issue of the journal Nature.

Crucial to the research was the use of an isotope of bohrium with a relatively long half-life, over 15 seconds, first detected last year by researchers at the U.S. Department of Energy's Lawrence Berkeley National Laboratory and the University of California at Berkeley.

"Elements beyond 100 are made an atom at a time, with very low production rates, and have very short half lives," says Darleane C. Hoffman, a longtime collaborator with Gaggeler's team and coleader of the group which identified long-lived bohrium 267 at Berkeley Lab's 88-Inch Cyclotron. A member of Berkeley Lab's Nuclear Science Division, Hoffman is a professor of chemistry at UC Berkeley and a leader in developing techniques for doing chemistry with single atoms.

To create bohrium 267 at PSI's PHILIPS cyclotron, the research team used a beam of neon 22 to bombard a target of berkelium 249, which has a half-life of 320 days. The targets were prepared at Berkeley Lab from material furnished by the Department of Energy through its Transplutonium Element Production Program at Oak Ridge National Laboratory.

Immediately after bombardment, the reaction products were swept into an automated system where they formed molecules in oxygen-containing hydrogen chloride gas. These oxychlorides were then passed through a chromatography column, in which the more volatile species pass through at lower temperatures.

During the month-long experiment, about three atoms of bohrium were created for each day of beam time, but only six bohrium nuclei were actually detected. The bohrium 267 compound was shown to be volatile at 180 degrees Celsius, behaving much like its periodic-table relatives technetium and rhenium.

"Chemical characterization of bohrium (element 107)," by H. W. Gaggeler, W. Bruchle, R. Dressler, D. C. Hoffman, A. Vahle, A. B. Yakushev, and others appears in Nature, vol 406, 7 September 2000. Besides Hoffman, the collaborating team at Berkeley included Berkeley Lab senior scientists Kenneth Gregorich and Heino Nitsche, a professor of chemistry at UC Berkeley, as well as postdoctoral fellows Uwe Kirbach and Carola Laue and graduate students Joshua Patin, Dan Strellis, and Philip Wilk.

In addition to PSI, the University of Bern, Berkeley Lab, and UC Berkeley, participating institutions included the Flerov Laboratory in Russia, the Forschungzentrum Rossendorf, Gesellschaft für Schwerionenforschung, and Technical University of Dresden in Germany, and the Japan Atomic Energy Research Institute in Japan.

The Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California.