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.