Discovery of Na 39

Abstract

© 2022 American Physical Society. The new isotope Na39, 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 Ca48 beam at 345 MeV/nucleon on a beryllium target. Projectile fragments were separated and identified in flight with the large-acceptance two-stage separator BigRIPS. Nine Na39 events have been unambiguously observed in this work and clearly establish the particle stability of Na39. Furthermore, the lack of observation of Ne35,36 isotopes in this experiment significantly improves the overall confidence that Ne34 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 Na39 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 Na39 at the neutron number N=28, which is normally a magic number.