Systematical properties of spontaneous fission for superheavy nuclei and a limit of existence of nuclei

Koura, Hiroyuki   ; Chiba, Satoshi

We present potential energy surfaces and partial half-lives of spontaneous fission with the use of the KTUY nuclear mass formula in the heavy- and super heavy nuclidic region. In this framework the deformed liquid-drop energy is calculated in the six-dimensional numerical integrals instead of the previous calculation by using an explicit form of the Legendre expansion with respect to deformation parameters. This improvement gives us capable to calculate nuclear shell energies in the wider deformation space from the ground-state shape to the nuclear fission. The theoretical spontaneous-fission half-lives in this calculation gives an upper limit of the proton number Z for nuclei with total half-lives of 1 nanosecond or more in the super heavy region around N=184, approximately Z=130-136. The predicted upper limit of Z for nuclei with those of 1 second is approximately Z=115. The border of existence of nuclei in the neutron-poor region is given not by the limit of proton emission, but by that of spontaneous fission.