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Title: Location of the neutron drip line beyond neon
Plain: 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: 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.
Settled by: Production cross-section measurements at FRIB at full beam power and at the RIKEN RIBF establishing non-observation limits for the next isotopes.
Kind: well-posed
Answer type: identification
References: (empty)
Literature status: open
Status note: RIKEN reported 39Na as bound (around 2022-2023); the drip line for $Z \ge 11$ remained unestablished as of 2026.
Posed since: (empty)