Systematics of α-preformation factors in closed-shell regions

The alpha-preformation factors of medium and heavy-mass nuclei are calculated by using the cluster-formation model. The obtained preformation factors of even-even, odd-A, and odd-odd nuclei consist in both magnitude and trend with the general features predicted by standard calculations. The variation of alpha clustering affected by the evolution of nuclear structure is observed from different behaviors of preformation factors. We typically analyze the variation of preformation factors in the closed-shell N = 126 and Z = 82 regions, and discuss in detail the structural effects on alpha-cluster formation. This work shows the strong correlation between a-preformation factors and the shell structure, which would be a useful reference for microscopic cluster-model calculations of alpha-decay half-lives.