Correlations between neutrons and protons near Fermi surface and $Q_{\alpha }$ of super-heavy nuclei

The shell corrections and shell gaps in nuclei are systematically studied with the latest Weizs"acker-Skyrme (WS4) mass model. We find that most of asymmetric nuclei with (sub)-shell closures locate along the shell stability line (SSL), $N=1.37Z+13.5$, which might be due to a strong correlation between neutrons and protons near Fermi surface. The double magicity of nuclei ${}^{46}$Si and ${}^{78}$Ni is predicted according to the corresponding shell gaps, shell corrections and nuclear deformations. The unmeasured super-heavy nuclei ${}^{296}$118 and ${}^{298}$120, with relatively large shell gaps and shell corrections, also locate along the SSL, whereas the traditional magic nucleus ${}^{298}$Fl evidently deviates from the line. The $\alpha$-decay energies of super-heavy nuclei with $Z=113-126$ are simultaneously investigated by using the WS4 model together with the radial basis function corrections. For super-heavy nuclei with large shell corrections, the smallest $\alpha$-decay energy for elements $Z=116$, 117 and 118 in their isotope chains locates at $N=178$ rather than $184$.