First observation of an excited state in the neutron-rich nucleus ${}^{31}\mathrm{Na}$

The first excited state in the neutron-rich N=20 isotope ${}^{31}\mathrm{Na}$ was observed at 350(20) keV via intermediate energy heavy-ion scattering, which is dominated by the Coulomb excitation mechanism. This state appears to be a rotational excitation built on a strongly deformed ground state. The yield of the γ ray deexciting this state can be reproduced by a shell model calculation which takes $\nu {(f}_{7/2}{,p}_{3/2})$ intruder configurations into account.