Precision mass measurements of very short-lived, neutron-rich Na isotopes using a radio-frequency spectrometer

Mass measurements of high precision have been performed on sodium isotopes out to ${}^{30}\mathrm{Na}$ using a new technique of radio-frequency excitation of ion trajectories in a homogeneous magnetic field. This method, especially suited to very short-lived nuclides, has allowed us to significantly reduce the uncertainty in mass of the most exotic Na isotopes: a relative error of $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ was achieved for ${}^{28}\mathrm{Na}$ having a half-life of only 30.5 ms and $9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ for the weakly produced ${}^{30}\mathrm{Na}.$ Verifying and minimizing binding energy uncertainties in this region of the nuclear chart is important for clarification of a long-standing problem concerning the strength of the $N=20$ magic shell closure. These results are the fruit of the commissioning of the new experimental program MISTRAL.