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GSI scientists hold world record for discovery of atomic nuclei



The GSI researchers Gottfried Münzenberg and Hans Geissel have discovered the largest number of atomic nuclei. Münzenberg, a professor at Johannes Gutenberg University Mainz, holds the world record with a total of 218 atomic nuclei. Geissel, a professor at Justus Liebig University Giessen, holds second place with 210 nuclei. That’s the result of a count carried out by Michael Thoennessen, a researcher at Michigan State University in the USA. He is currently working on the history of the discovery of atomic nuclei and has published these numbers in the scientific journal Nature.

The matter of our earth is made of atoms. All atoms with the same electric charge in their nuclei are classified as being nuclei of the same chemical element. To date, we know of 114 such chemical elements. Each element comes in different types known as isotopes, whose atomic nuclei have the same electrical charge but different masses. The discovery of a new atomic nucleus is thus also the discovery of a new isotope. Researchers have observed around 3,100 different isotopes, and another thousand as yet unknown ones are forecast to exist.

Especially heavy or especially light isotopes of an element are particularly interesting for scientists. They play a major role in our understanding of how the elements are created in stars and in stellar explosions. However, because of their short lifetimes they do not occur naturally on earth. Scientists such as Münzenberg and Geissel therefore attempt to create and analyze them in the laboratory. They do this by accelerating atomic nuclei and colliding them with material samples. New isotopes occur as fragments resulting from the collisions. These new isotopes can be sorted out and studied with the help of separators at the GSI accelerator facility.

“We started creating isotopes in 1977. We were incredibly excited as we recognized the first new nuclei on the basis of how they decayed,” says Münzenberg, who has retired since then. “We want to discover where the frontiers of the nuclide landscape lie. Where else can matter exist? And what shape are the nuclei? We want to find many of these exotic nuclei in order to get an idea of the landscape, and then to study the interesting ones.” Münzenberg was pleasantly surprised to hear of his world record. Although he knew he had made a major contribution to the field, he hadn’t kept track of the exact number of nuclei.

Third place is occupied by the pioneer of nuclear mass determination, Francis William Aston of Cambridge, who received the 1922 Nobel Prize in Chemistry for his isotope discoveries. He identified many—207 in total—of the naturally occurring isotopes at the start of the 20th century. Other GSI scientists are catching up with him, however. Peter Armbruster, for example, is in fourth position. The list of the top 25 isotope discoverers includes 22 who have carried out research at GSI.

Working together with his students, Thoennessen has created a summary of the discoverers of all isotopes by person and by laboratory on the basis of scientific publications. He regards an isotope as being recognized when its mass and charge have been measured and published. The Lawrence Berkeley National Laboratory in Berkeley, California, is the leading laboratory in the statistics, with 635 discovered isotopes. GSI comes in second here, with 372 isotopes discovered.

Münzenberg’s world record will very probably be exceeded when the accelerator centre Fair (Facility for Antiproton and Ion Research) at GSI starts operating in the coming years. At Fair it will be possible to create many new isotopes within a very short time.

Additional information about Michael Thoennessen’s isotope research is available from: http://www.nscl.msu.edu/~thoennes/isotopes/

Fragment separator
Chart of nuclides
Foto: A. Zschau, GSI Helmholtzzentrum für Schwerionenforschung
Source: GSI Helmholtzzentrum für Schwerionenforschung