Abstract
The calculations were carried out using an energy-dependent formula, where the superheavy-nuclei mass defect was evaluated by using both the KTUY05 and WS4 nuclear mass formulae. This formula reproduced successfully the value of Po-212 calculated from a combined microscopic shell and cluster model and described satisfactorily the alpha decay of heavy nuclei. The values of the preformation probability and the cluster formation energy, and their dependence on the neutron number, confirmed the shell and subshell closures and the similarities of alpha clustering between heavy and superheavy nuclei. The calculations carried out with the WS4 mass formula showed larger alpha-clustering effects than the KTUY05.