Evidence for the extinction of the N=20 neutron-shell closure for 32Mg from direct mass measurements
The "island of inversion" around 32Mg is one of the most important paradigms for studying the disappearance of the stabilizing "magicity" of a shell closure. We present the first Penning-trap mass measurements of the exotic nuclides 29‑31Na and 30‑34Mg, which allow precise determination of the empirical shell gap for 32Mg. The new value of 1.10(3) MeV is the smallest observed shell gap for any nuclide with a canonical magic number.