Background: The synthesis of superheavy elements (SHEs) beyond Oganesson, such as $Z=119$, remains a formidable challenge, primarily because the dominant quasifission (QF) channel severely hinders the formation of compound nuclei. A microscopic understanding of the QF dynamics is therefore essential for guiding future experiments.

Purpose: We investigate the microscopic mechanisms of QF in the ${}^{54}\mathrm{Cr}+{}^{243}\mathrm{Am}$ reaction, a key candidate system for synthesizing SHE 119, with particular emphasis on the roles of projectile orientation and incident energy.

Method: The calculations are performed using the fully microscopic time-dependent Hartree-Fock theory based on the Skyrme energy density functional. We perform systematic simulations covering a broad set of initial orientations of the deformed ${}^{54}\mathrm{Cr}$ and ${}^{243}\mathrm{Am}$ nuclei, together with a finely spaced range of incident energies extending from below to well above the Coulomb barrier.

Results: Our fixed-energy simulations show that projectile side collisions are strongly shell driven, with heavy and light fragments tending toward the spherical $Z=82$ and deformed $N=52–56$ shell regions, respectively, whereas tip collisions exhibit weaker shell influence. These shell-driven reactions are associated with shorter contact times, consistent with faster neck rupture caused by the enhanced rigidity of shell-stabilized fragments. In the tip-tip channel, the energy dependence further reveals a transition from an octupole-deformed region around $Z\approx 88$ to a spherical shell-driven regime at higher energy, while shell steering is comparatively weak in a near-barrier region at a center-of-mass energy of approximately 226 MeV.

Conclusions: Our microscopic study demonstrates that the manifestation of shell effects in the final QF fragment distributions is a dynamical outcome sensitively dependent on both the initial collision geometry and the incident energy. This pronounced energy dependence indicates that the competition between QF and fusion may be affected by the beam energy. The comparatively weak shell steering found in the near-barrier tip-tip region therefore suggests a possible low-energy window of potential interest for SHE synthesis.

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• Low & intermediate energy heavy-ion reactions
• Models & methods for nuclear reactions
• Nuclear reactions
• Synthesis of new superheavy elements