The $\alpha$-decay energy ($Q_{\alpha }$), deduced from nuclear binding energies, is often utilized to study nucleon-nucleon interaction and explore the structural property of exotic nuclei near the proton dripline. The systematics of available experimental $\alpha$-decay energies, in isotopic chains of heavy nuclei across the $N=126$ shell, behaves in a seeming contradiction with the shell-model picture: the lowest value of $Q_{\alpha }$ occurs at $N=124$, not $N=126$. This phenomenon can be effectively explained by investigating the mass differences, with the concentration on the contributions from the shell effect and pairing correlation through the macroscopic-microscopic mass model. The analysis is then extended to the region near the subshells of both $N=152$ and $N=162$, leading to the satisfactory reproduction of the experimental trend of decay energies as well. In addition, we present a detailed comparison with those results from the Finite-Range Droplet Model, the Hartree-Fock-Bogoliubov mass model, and the Weizsäcker-Skyrme mass formula, as accompanied by the similar pattern with respect to the experimental data.

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• Alpha decay
• Binding energy & masses
• Nuclear structure & decays
• Nucleon-nucleon interactions
• A ≥ 220