Systematical law of spontaneous fission half-lives of heavy nuclei

Systematic calculations on spontaneous fission half-lives of heavy nuclei are carried out by Swiatecki's formula with new parameters and by its generalized form. A new formula with only four parameters is also proposed for spontaneous fission half-lives. Experimental half-lives are well reproduced by the three formulas. We have found from systematic analysis of available data that there is a long lifetime line of spontaneous fission N=Z+52 for heavy elements with Zgreater than or equal to90. The new formula can be used to predict the spontaneous fission half-lives of heavy nuclei not far away from this long lifetime line. The small deviation between experimental half-lives and theoretical ones from the new formula is analyzed and discussed.