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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. |