Superheavy Nuclei

Abstract

The existence of nuclei at the limits of stability is determined by nuclear structure. The nuclear shell model, which effectively describes nuclear properties and the underlying shell structure all over the chart of nuclei, predicts the next closed shells or subshells beyond the double magic 208 Pb at proton numbers Z = 114, 120, or 126, and at neutron number N = 184. Although the strength of the shells is difficult to calculate, an increased stability is expected for nuclei having these numbers of protons and neutrons. Experiments performed at various major laboratories were aiming to produce these “superheavy nuclei.” Described are the results of these experiments covering reaction studies and measurements of the decay properties of the nuclei produced. A comparison of the data with predictions of theoretical models reveals an increased stability for deformed nuclei at Z = 108 and N = 162, and for spherical nuclei having proton numbers Z = 114–118 and neutron numbers approaching N = 184. It is shown that, in general, the theoretical predictions are confirmed by experiments, although details of the structure of the island of superheavy nuclei remain to be explored.

Fission barriers at the end of the chart of the nuclides

“…We show as black dots those nuclei for which spontaneous fission has been observed with a half-life less than 30 days, taken from the compilation of Ref. [59]. The aim is to investigate what correlations we find between the calculated barrier heights and the observed fissioning nuclei.…”