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 $5\times {10}^{-7}$ was achieved for ${}^{28}\mathrm{Na}$ having a half-life of only 30.5 ms and $9\times {10}^{-7}$ 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 $N=20\mathrm{}$ magic shell closure. These results are the fruit of the commissioning of the new experimental program MISTRAL.

• Received 24 April 2001

DOI:https://doi.org/10.1103/PhysRevC.64.054311