The most important theoretical developments leading to the current understanding of heavy-element stability

Abstract

AbstractWe discuss the sequence of developments that over the past 90 years led to current insights on heavy-element stability. The semi-empirical mass model, and its extension to deformed shapes, developed in the period 1936–1950 allowed the interpretation of nuclear fission. Around 1950 the spherical single-particle model was developed, soon after with extension to deformed nuclei. Speculations about a shell-stabilized region of spherical heavy elements near $$Z=126$$ Z = 126 were made. In the 1960ies Strutinsky combined the single-particle and macroscopic liquid-drop models into a unified picture, the shell-correction, or macroscopic-microscopic method. Now it was also realized that although $$Z=126$$ Z = 126 was present, an often stronger spherical gap in calculated proton single-particle level diagrams, $$Z=114$$ Z = 114 , was also present, but its significance had previously been overlooked. A large number of studies of the stability of nuclei in the “shell-stabilized” region surrounding $$Z=114$$ Z = 114 and $$N=184$$ N = 184 followed. Initially the assumption was that elements just beyond the actinides, would be too unstable to be observed. The 1970ies saw considerable work in refining the initial single-particle and macroscopic models. This set the stage for global studies, which took off in the 1980ies and have continued until today. The more accurate nuclear-structure models allowed calculations of masses, decay-chain properties and branching between different decay modes to useful accuracy and predictive quality. A completely unexpected result was that the calculations showed the existence of an area of relatively stable deformed nuclei in the presumed “sea of instability” between the actinides and the next postulated spherical magic numbers.