Location of the neutron drip line beyond neon
In plain words
The neutron drip line marks the heaviest isotope of each element that holds on to all its neutrons. It has been mapped experimentally only up to neon, element 10.
Precise statement
For $Z=11 \text{ to } 20$ (sodium to calcium), determine the most neutron-rich isotope bound against one- and multi-neutron emission. 31F and 34Ne are the heaviest bound F and Ne isotopes (Ahn et al., PRL 2019), and 39Na has been observed as bound. Answer: the drip-line nucleus for each $Z$ from Na to Ca, with experimental evidence that the next isotopes are unbound.
What would settle it
Production cross-section measurements at FRIB at full beam power and at the RIKEN RIBF establishing non-observation limits for the next isotopes.
Status in the literature
Unverified note
RIKEN reported 39Na as bound (around 2022-2023); the drip line for $Z \ge 11$ remained unestablished as of 2026.