An ‘alpha-decay without tunnelling’ approach shows that alpha-preformation probability in trans-lead even-even alpha-emitters lies in the range of 0·17–0·08, indicating a clear shell-closure effect atN = 126 and exhibits appreciably enhanced values in open-shell nuclei and executes a zig-zag nature with increasing neutron number in an isotopic series. All these findings are in fair qualitative agreement with experimental observations. Experimental results are found to overestimate this parameter for these heavy deformed nuclei.

With the help of a plot of logarithmic experimental α-decay half-life of even-even α-emitters versus the fissility parameter, it is demonstrated that α-decay is a distinct type of spontaneous fission. A simple empirical relation between experimental α-decay half-life and the fissility parameter is also given. A close examination of the nature of dependence of α-decay half-life on fissility parameter reveals that Coulomb repulsive energy accelerates the process of α-decay rather than retard it.