Energy levels with spin-orbit splitting — magic numbers 2, 8, 20, 28, 50, 82, 126
The nuclear shell model (Mayer, Jensen 1949; Nobel 1963) explains magic numbers via spin-orbit coupling: the ℓ·s interaction splits each orbital into j = ℓ±½ sub-shells, lowering the j = ℓ+½ level significantly. This reordering creates large gaps at N,Z = 2, 8, 20, 28, 50, 82, 126 — nuclei with these nucleon numbers are exceptionally stable, analogous to noble gases in atomic physics.