Since more than five years scientists at the Flerov Laboratory for Nuclear Reactions in Dubna, Russia, produce in nuclear fusion reactions isotopes, which they attribute to the island of super heavy atoms, theoretically predicted many years ago. This island is separated from the known elements not only according to the number of protons (atomic number) but also according to the number of neutrons (isotopes) in their atomic nuclei. So far, several attempts to reproduce these observations in purely physics experiments at the Lawrence Berkeley National Laboratory, Berkeley, USA failed. The observed low production rates of several atoms per week for these new elements artificially produced using a heavy ion accelerator for irradiations of radioactive materials as uranium, plutonium, americium, curium, or californium with high energy beams of calcium represent a big technical challenge for the scientists.
In collaboration between the University of Bern, the Paul Scherrer Institute, the Flerov Laboratory in Dubna, Russia and the Institute of Electron Technology in Warsaw, Poland, in a beam time of three weeks duration at the Dubna U-400 cyclotron a plutonium target with the mass number 242 was irradiated by highly intense beams of calcium with the mass number 48. According to earlier observations element 114 is formed by nuclear fusion. The produced isotope of element 114 with the mass number 287 decays in less than a second to the isotope 283 of element 112, for which the half-life was reported to be about 4 s. This is long enough to perform chemical investigations. Hence, the experiment aimed at the first independent confirmation of the production of element 112 in this nuclear reaction and, additionally, at its chemical investigation. Theoretical calculations predict for element 112 a chemical behavior between mercury, a volatile heavy metal, and radon, a noble gas. Therefore, these elements were both simultaneously investigated in this experiment.
Indeed, the decay of two atoms of element 112 was observed on May, 11 2006 at 02:40:50 and on May, 25 2006 at 08:37:11 (Moscow time). Their decay patterns are unambiguously consistent with decay properties reported earlier: The observed atoms of element 112 decayed by an alpha-particle emission with a energy of 9.5 million electron volts into the isotope of element 110 with the mass number 279, which decayed about 0.5 seconds later by spontaneous fission. As expected, th observed energies of both fission fragments were much higher than the energies of the well known fission of Uranium with the mass number 235, as it is used nuclear power plants. Interestingly these single atoms of element 112 behaved in the experiment more similar to mercury rather than to radon. This information is deduced from the observation that along 32 gold covered detectors, held at different temperatures, the decay of element 112 was registered on detectors, where mercury was deposited and not radon.
This work was carried out in the group of Prof. Heinz W. Gäggeler.