Collapse of the conventional shell-model ordering in the very-neutron-rich isotopes of Na and Mg

Recent experimental data on the structure of the very-neutron-rich isotopes of Na and Mg show sharp departures at $N=20$ from the predictions of conventional d5/2-s1/2-d3/2 shell-model calculations.NUCLEAR STRUCTURE Isotopes of Na and Mg; calculated ground state energies, magnetic dipole moments, and excitations of 2⁺ states; 0d5/2-1s1/2-0d3/2 shell model, Chung-Wildenthal Hamiltonians.