With the help of novel techniques developed at the Department of Energy's Lawrence Berkeley National Laboratory, an international team of scientists has performed the first chemical studies of element 108, hassium, the heaviest element whose chemistry has yet been studied.
The researchers established that hassium forms a gaseous oxide similar to that of osmium, confirming that hassium, like osmium, is a member of group 8 of the periodic table and should be placed directly under it.
Heino Nitsche of Berkeley Lab's Nuclear Science and Chemical Sciences Divisions, who is also a professor of chemistry at the University of California at Berkeley, directed the development of a new, very low temperature technique for separating and detecting oxides from group 8.
Full scale experiments using the technique were performed on osmium oxides at Berkeley Lab's 88-Inch Cyclotron, but the necessary weeks of beam time for the hassium experiments were only available in Europe.
"To achieve these exciting advances in the chemistry of the heavy elements requires many hours of accelerator time -- plus lots of 'people power' to prepare and monitor the experiments constantly," Nitsche remarks. "The only practical way to achieve this is through international collaboration."
Postdoctoral fellow Uwe Kirbach of the Nuclear Science Division helped colleagues at the Paul Scherrer Institute and the University of Bern in Switzerland build a version of the Berkeley Lab detector, which was installed at the UNILAC heavy ion accelerator at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Germany.
(Hassium was discovered at GSI in 1984; its name comes from Hassias, Latin for Hesse, the state where Darmstadt is located.)
Hassium does not exist in nature, but must be created one atom at a time by fusing lighter nuclei. At GSI's UNILAC, energetic magnesium-26 projectiles bombarded targets of curium-248, a rare artificial isotope prepared for the experiment at the Institute of Nuclear Chemistry in Mainz, Germany.
Multiple curium targets were mounted in a rotating wheel system developed at GSI. The hassium atoms formed by impacts between target and beam reacted with oxygen to form hassium oxide molecules. The single molecules were carried through the detector by a stream of helium and immediately condensed on semiconductor diodes, arranged in rows and maintained at temperatures graded from minus 20 to minus 170 degrees Centigrade.
Hassium oxide was found to condense at a higher temperature than osmium oxide, indicating that it is less volatile. The successful chemical separation of hassium points the way to techniques that will be useful in studying the chemistry of the recently discovered elements 118 and 116, which are also predicted to be gaseous elements.
Press releases, in German, detailing the chemical studies of hassium may be found on the websites of GSI and of the Paul Scherrer Institute.
In addition to Nitsche and Kirbach, members of the Berkeley Lab/UC Berkeley team that participated in the chemical studies of element 108 include Cody Folden, Tom Ginter, Ken Gregorich, Diana Lee, Victor Ninov, Jon Petter Omtvedt of the University of Oslo, Joshua Patin, N.K. Seward of the University of Surrey, Dan Strellis, Ralf Sudowe, Philip Wilk, Peter Zielinski, and Darleane Hoffman.
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. - By Paul Preuss
[Contact: Professor Heino Nitsche, Paul Preuss]