Nuclei at the Borderline of Their Existence

Abstract

Throughout the 60 years that have passed since the discovery of the first man-made elements, neptunium and plutonium, investigations in the field of synthesis of new elements and of their properties have become one of the most important and rapidly developing fields in nuclear physics and chemistry. The transition from conventional methods of neutron capture for producing manmade elements to methods employing heavy-ion reactions has made it possible to synthesize many elements heavier than fermium (Z = 100). In the mid-1960s, a theoretical description of the masses and fission barriers for new nuclei led to the prediction of islands of stability of heavy and super-heavy nuclides near the closed proton and neutron shells. The results of the first experiments devoted to the synthesis of heaviest nuclides formed in nuclear reactions induced by ⁴⁸Ca ions are presented. For various individual nuclei, the observed decay chains consisting of successive events of alpha decay and ending in spontaneous fission, as well as the decay energies and lifetimes, are consistent with the predictions of theoretical models that describe the structure of heavy nuclei. These data furnish the first indication of the existence of superheavy elements being highly stable with respect to different decay modes.

The experiments in question employed the heavy-ion accelerator installed at the Flerov Laboratory for Nuclear Reactions at the Joint Institute for Nuclear Research (JINR, Dubna, Russia). They were performed in collaboration with physicists from the Lawrence Livermore National Laboratory (Livermore, USA); the Gesellschaft für Schwerionenforschung (GS1, Darmstadt, Germany); RIKEN (Saitama, Japan), the Institute of Physics and Department of Physics, Comenius University (Bratislava, Slovak Republic), and the Dipartimento di Fisica, Università di Messina (Messina, Italy).