Background: Fragment shell effects are central to the formation of spontaneous-fission (SF) mass yields. However, it remains unclear which configurations favored by fragment shell effects are dynamically selected and ultimately appear as peaks in the SF yields.

Purpose: To clarify, by comparing ${}^{240}\mathrm{Pu}, {}^{232}\mathrm{Th}$, and ${}^{264}\mathrm{Fm}$, how the potential-energy surface (PES) topology and the fission dynamics in the classically allowed region select the scission configurations in which fragment shell stabilization is reflected in the SF yield peaks.

Method: A two-step microscopic framework is employed. The PES and collective inertia are obtained from constrained Hartree–Fock–Bogoliubov calculations. The first step, from the inner to the outer turning points, is treated within the Wentzel–Kramers–Brillouin approximation along the least-action path. The second step, from the outer turning points to scission in the classically allowed region, is described by Langevin dynamics. Fragment shell effects are analyzed through fragment PES and smoothed level density indicators evaluated for representative even-even fragment pairs selected from the Langevin scission configurations.

Results: The calculated yields display a two-component asymmetric pattern in ${}^{240}\mathrm{Pu}$, a less distinctly separated asymmetric pattern in ${}^{232}\mathrm{Th}$, and a symmetric peak in ${}^{264}\mathrm{Fm}$. The fragment shell analysis shows that the larger yield components coincide with a coherent overlap among dynamically populated scission configurations, favorable fragment PES regions, and regions of low neutron and/or proton level density near the Fermi surface. This overlap is most evident in the dominant asymmetric components of ${}^{240}\mathrm{Pu}$ and ${}^{232}\mathrm{Th}$ and in the symmetric component of ${}^{264}\mathrm{Fm}$, whereas the subdominant components show weaker or more diffuse overlap.

Conclusion: SF yields reflect shell-favored fragment configurations that are made accessible by the PES topology and populated by the Langevin dynamics. Enhanced yields then arise in shell-stabilized channels, where shell gaps provide additional binding and favor the fragment configurations energetically. Proton shell effects play a key role in heavy and light fragments, while neutron shell effects provide additional stabilization.

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• Fission
• Scission point
• A ≥ 220
• Nuclear density functional theory
• Nuclear many-body theory