Evidence for the extinction of the N=20 neutron-shell closure for 32Mg from direct mass measurements

The island of inversion around Mg-32 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 Na29-31 and Mg30-34, which allow precise determination of the empirical shell gap for Mg-32. The new value of 1.10(3) MeV is the smallest observed shell gap for any nuclide with a canonical magic number.