Background: The experiment of ${}^{180}\mathrm{Hg}$ fission revealed a possible “new asymmetric fission mode” in the preactinide region, posing challenges to current fission theory. Similarity in shell effects is observed between fission and quasifission, providing the possibility for widely exploring the topography of a fission potential-energy surface (PES).

Purpose: We aim to investigate the shell effects in the quasifission toward ${}^{180}\mathrm{Hg}$ and to explore their connection with the ${}^{180}\mathrm{Hg}$ fission.

Method: ${}^{68}\mathrm{Zn}+{}^{112}\mathrm{Sn}$, ${}^{74}\mathrm{Se}+{}^{106}\mathrm{Pd}$, ${}^{80}\mathrm{Kr}+{}^{100}\mathrm{Ru}$, and ${}^{84}\mathrm{Kr}+{}^{96}\mathrm{Ru}$ central collisions at different energies and projectile orientations are calculated using the Skyrme time-dependent Hartree-Fock approach. The static fission properties are calculated with the constrained Hartree-Fock-Bogoliubov method and compared with the quasifission results.

Results: Shell effects are found to hinder mass equilibration between the prefragments, enhancing the production of fragments near the $80/100$ mass split. By comparing the quasifission trajectories with the PES in the $(Q_{20},Q_{30})$ space, the role of the PES ridge in forming fragments is identified. The presence of the asymmetric valley causes the ${}^{68}\mathrm{Zn}+{}^{112}\mathrm{Sn}$ quasifission to exhibit a prefragment mass equilibration process and scission-point configuration similar to those of ${}^{180}\mathrm{Hg}$ fission. The elongated light fragment is found to be a key factor in reproducing the experimental fission total kinetic energies. Meanwhile, a more pronounced proton shell gap is found in the ${}^{68}\mathrm{Zn}+{}^{112}\mathrm{Sn}$ quasifission compared with other reactions.

Conclusions: By using quasifission dynamics as a probe of the fission pathway, the present calculations help clarify the specific influence of the PES topography and provide support for the dominance of proton shell effects and light fragment deformation in preactinide fission.

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• Fission
• Heavy-ion reaction mechanisms
• Low & intermediate energy heavy-ion reactions
• Models & methods for nuclear reactions
• Nuclear reactions
• 150 ≤ A ≤ 189