  Multinucleon transfer processes in low-energy heavy ion reactions have
attracted increasing interest in recent years aiming at production of new
neutron-rich isotopes. Clearly, it is an imperative task to further develop
understanding of underlying reaction mechanisms to lead experiments to success.
In this paper, from systematic time-dependent Hartree-Fock calculations for the
$^{238}$U+$^{124}$Sn reaction, it is demonstrated that transfer dynamics depend
strongly on the orientations of $^{238}$U, quantum shells, and collision
energies. Two important conclusions are obtained: (i) Experimentally observed
many-proton transfer from $^{238}$U to $^{124}$Sn can be explained by a
multinucleon transfer mechanism governed by enhanced neck evolution in tip
collisions; (ii) Novel reaction dynamics are observed in tip collisions at
energies substantially above the Coulomb barrier, where a number of nucleons
are transferred from $^{124}$Sn to $^{238}$U, producing transuranium nuclei as
primary reaction products, that could be a means to synthesize superheavy
nuclei. Both results indicate the importance of the neck (shape) evolution
dynamics, which are sensitive to the orientations, shell effects and collision
energies, for exploring possible pathways to produce new unstable nuclei.
