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No known nucleus has reached 184 neutrons.","posed_since":"","precise":"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.","problem_ref":null,"references":"","settled_by":"Synthesis, for example through multinucleon-transfer reactions, of superheavy nuclei with $N \\ge 180$ and measurement of their decay chains.","status_note":"The most neutron-rich known superheavy nuclei reach $N = 177$ ($294\\mathrm{Ts}$), seven neutrons short of 184, as of 2026.","title":"Next spherical proton shell closure in superheavy 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