Calculation of half-lives for superheavy nuclei

Abstract

We have performed a new calculation of the half-lives of superheavy nuclei with respect to spontaneous fission, α-decay and β-decay (including electron capture). The half-lives are calculated from fission barriers and decay energies that have been obtained by means of the macroscopic-microscopic method applied to realistic diffuse-surface single-particle potentials. The results indicate that the longest total half-life is 10 9.4 y for the nucleus 294110, which decays predominantly by the emission of α-particles. As a general rule, the predominant decay mode is α-emission for nuclei containing more than 110 protons or a few more neutrons than 184, β-emission for nuclei containing less than 110 protons, and spontaneous fission for nuclei containing either less than 184 neutrons or substantially more. Therefore, if nuclei in the vicinity of 304122 could be formed successfully in their ground states, they should decay primarily by the rapid emission of a series of high-energy α-particles, which provides a simple identification method. However, once the closed proton shell at Z = 114 is reached, electron capture becomes the predominant decay mode. This leads to nuclei whose calculated total half-lives are sufficiently long that they could be studied by conventional chemical methods. Some fission barriers along the r-process path have been calculated for two sets of liquid-drop-model constants that differ primarily in their values of the surface-asymmetry constant K. For K = 2.84, which is representative of the values suggested by a variety of new evidence, the potential barrier against fission has practically disappeared for nuclei in the vicinity of mass number 290. The neutron-induced fission of such nuclei should be extremely rapid, thus terminating the r-process somewhat before the island of superheavy nuclei is reached.