How Far does the Area of Superheavy Elements Extend? : Decay Modes of Heavy and Superheavy Nuclei Predicted by a Mass Formula(Science around Superheavy Elements)

Abstract

Nuclear decay modes for heavy and superheavy nuclei are discussed with the use of a nuclear mass formula and some decay models. This mass formula, which we refer to as the KTUY formula, is composed of a gross part expressed as a smooth function of proton number and neutron number and a shell part calculated from single-particle potentials. On estimations of decay modes excluding spontaneous-fission, we use Q-values of the KTUY mass formula. The spontaneous fission half-lives are estimated from penetrability on a potential energy surface derived from a method of calculating shell energies of the KTUY mass formula. We indicate some regions of unknown nuclei with spontaneous-fission dominance and show the "island of stability" in the region of superheavy nuclei. We also point out a possibility of existence of another region of the island of stability beyond the superheavy region. In these regions, spontaneous-fission is very important to determine the border of existence of nuclei.