On three topical aspects of the N = 28 isotonic chain

The evolution of single-particle orbits along the N = 28 isotonic chain is studied within the framework of a relativistic mean-field approximation. We focus on three topical aspects of the N = 28 chain: (a) the emergence of a new magic number at Z = 14; (b) the possible erosion of the N = 28 shell; and (c) the weakening of the spin-orbit splitting among low-j neutron orbits. The present model supports the emergence of a robust Z = 14 subshell gap in 48Ca, that persists as one reaches the neutron-rich isotone 42Si. Yet the proton removal from 48Ca results in a significant erosion of the N = 28 shell in 42Si. Finally, the removal of s1/2 protons from 48Ca causes a ∼50% reduction of the spin-orbit splitting among neutron p-orbitals in 42Si