Exotic Isotopes of Magnesium

The structure of nuclei in the vicinity of expected nuclear shell closures away from stability has been, and continues to be, a cornerstone for nuclear structure study.  The confirmation of certain ‘magic numbers’ in exotic nuclei provides insight into the evolution of nucleon configurations with isospin, but perhaps even more light is shed into the structure of the atomic nucleus when expected shell closures are found to be weakened, or entirely disappear.  The competition between monopole shifts of single particle energies and pairing plus quadrupole correlations leads to competition between spherical and deformed configurations.  Around ³²Mg the change in effective single particle spacing reduces the N=20 shell gap and the deformed intruder configuration, with neutron pairs promoted from the sd to the fp shell, is energetically favoured.  Recent experimental work in the Mg isotopes has suggested a chain of prolate-deformed nuclei along Z=12, extending to N=28 and ⁴⁰Mg, where there is a similar development of deformation along the isotonic chain below ⁴⁸Ca, with the removal of protons driving rapid shape oscillations between the N=28 nuclei.

I will give an overview of our knowledge in this part of the nuclear landscape, and discuss the latest experimental results in this region between N=20 and N=28, focusing on the Mg isotopes, and the evolution of their structure with spin, isospin and binding energy.