The new isotope ${}^{39}\mathrm{Na}$, the most neutron-rich sodium nucleus observed so far, was discovered at the RIKEN Nishina Center Radioactive Isotope Beam Factory using the projectile fragmentation of an intense ${}^{48}\mathrm{Ca}$ beam at $345\mathrm{MeV}/\text{nucleon}$ on a beryllium target. Projectile fragments were separated and identified in flight with the large-acceptance two-stage separator BigRIPS. Nine ${}^{39}\mathrm{Na}$ events have been unambiguously observed in this work and clearly establish the particle stability of ${}^{39}\mathrm{Na}$. Furthermore, the lack of observation of ${}^{35,36}\mathrm{Ne}$ isotopes in this experiment significantly improves the overall confidence that ${}^{34}\mathrm{Ne}$ is the neutron dripline nucleus of neon. These results provide new key information to understand nuclear binding and nuclear structure under extremely neutron-rich conditions. The newly established stability of ${}^{39}\mathrm{Na}$ has a significant impact on nuclear models and theories predicting the neutron dripline and also provides a key to understanding the nuclear shell property of ${}^{39}\mathrm{Na}$ at the neutron number $N=28$, which is normally a magic number.

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• Nuclear binding
• Nuclear structure & decays