 Neutron-rich magnesium shell-closure test

A 2013 RIKEN experiment used a fast calcium beam on beryllium, selected radioactive aluminium and silicon fragments, then struck carbon to produce magnesium isotopes with $N=22,24,26$. Emitted gamma rays supplied excitation energies; comparison across these isotopes supported deformation extending beyond the $N=20$ region toward $28$. This tests the limits of traditional magic numbers, not merely their arithmetic. The inferred shape depends on nuclear-structure interpretation of the energy levels, rather than direct imaging.^[ref]