Growth for league of super-heavy elements

Radiochemical evidence demonstrates existence of two new elements

Nuclear Research Center Dubna © PSI
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Two new heavy elements have been detected at the Russian nuclear research center in Dubna, the existence of which had previously only been theoretically postulated. The elements with atomic numbers 113 and 115 were identified using decay chains and radiochemical evidence developed by a Swiss research team.

Chemistry continues to penetrate into scientifically unknown areas. Uranium was the heaviest chemical element until 1940. The naturally occurring metal carries the atomic number 92, since 92 positively charged protons are present in its atomic nucleus. Since then, more than 20 artificially produced elements with higher atomic numbers have been discovered.

Birth of Element 115

Heavy elements decay via cascades of electrically charged helium atoms, called alpha particles. Such decay chains were used by American, Russian and Swiss scientists to experimentally prove elements 115 and 113, which until now had only been accepted theoretically and were still unnamed. For the synthesis of atoms of element 115, the researchers bombarded a rotating disk of americium, a transuran atomic number 95, with a calcium beam. In rare cases, nuclear mergers occurred: the birth of the new element 115.

But his existence was not proven. Its atoms live only a short time, about a tenth of a second, and are therefore difficult to detect. Whereas the physical detection of element 115 atoms by special detectors yielded only three hits in the past, the radiochemical path was five times more successful.

Radiochemical detection with 15 decay atoms

Element 115 decays with emission of an alpha particle first to element 113 and then over further emissions of alpha particles (helium nuclei) to dinium with atomic number 105. Here the elegant experimental proof of the research team of the Paul Scherrer Institute began: It installed behind the rotating americium disk a copper plate, which picked up the ejected element 115 atoms. display

If it proves that Dubnium atoms (with a half-life of 32 hours) can be detected after a certain time, the verification would be accomplished. In fact, the researchers were able to identify a total of 15 Dubnium atoms and thus successfully prove that the assumed decay chain actually exists. The physical evidence could be substantiated radiochemically.

"Swiss science was able to celebrate a premiere albeit abroad", reports Heinz G ggeler, head of research at the PSI and chemistry professor at the University of Bern, who headed the Swiss group. In the race for the constant expansion of the periodic table, Switzerland is also among the leaders for the first time. The experiments required, however, the heavy ion accelerator with the highest intensity of calcium radiation in the world. This facility is located in the Nuclear Research Center Dubna, 120 kilometers north of Moscow. More than 6, 000 people work in this huge research center on the banks of the Volga.

(Paul Scherrer Institute (PSI), 31.01.2006 - NPO)