RealNucleus — single-shell packing model (reduced)

One inner electron core of radius Re + Z electrons, surrounded by a single outer proton shell of 2Z protons. Shell thickness d = c/Z (proton size scales with electron attraction). Single shell holds all 2Z protons up to Z = Nmax/2; beyond, the model is silent.

Binding energy (single shell, exact algebra): E = Σ(−P·Z + P(P−1)/2)/r* = −Z/r* with r* = Re + c/(2Z). So |E/A| = s · 2.72 / (2 r*) MeV, depending only on c, Re, s. As Z grows, r* → Re, giving asymptote |E/A|∞ = s · 1.36 / Re.
Thickness constant c  (d=c/Z) = 0.50
Electron core radius Re = 0.15
Max protons per shell Nmax = 56
Core expansion γ (Reeff=Re+γ(Z−Zbreak)) = 0.0005
Energy scale s = 1.04
Highlight Z = 26
|E/A| vs Z (MeV/nucleon). Experimental B/A in grey (AME tables), single-shell model in blue.

Shell data (highlighted Z)