Next spherical proton shell closure in superheavy nuclei
In plain words
Theory predicts an 'island of stability' of unusually long-lived superheavy nuclei centred on a magic neutron number 184 and a proton number that models place at 114, 120 or 126. No known nucleus has reached 184 neutrons.
Precise statement
Determine which proton number $Z$ (114, 120 or 126) gives the next spherical shell gap above $Z = 82$ for $N$ near 184, from measured $\alpha$-decay $Q$ values, fission half-lives and spectroscopy of nuclei with $Z \ge 110$, and from theory with quantified spin-orbit and density-functional uncertainty. Answer: the $Z$ of the shell closure and the predicted half-life of the doubly magic nucleus.
What would settle it
Synthesis, for example through multinucleon-transfer reactions, of superheavy nuclei with $N \ge 180$ and measurement of their decay chains.
Status in the literature
Unverified note
The most neutron-rich known superheavy nuclei reach $N = 177$ ($294\mathrm{Ts}$), seven neutrons short of 184, as of 2026.