Theoretical study of effects of the entrance channel on the relative yield of complete fusion and quasifission in heavy-ion collisions within a dinuclear system approach

Abstract

The relative yield of complete fusion and quasifission components for the $^{12}\mathrm{C}+^{204}\mathrm{Pb}, ^{19}\mathrm{F}+^{197}\mathrm{Au}, ^{30}\mathrm{Si}+^{186}\mathrm{W}$, and $^{48}\mathrm{Ca}+^{168}\mathrm{Er}$ reactions which all lead to the compound nucleus $^{216}\mathrm{Ra}$ are analyzed to calculate the entrance channel effects by comparison of capture, complete fusion, and quasifission cross sections, emission barriers (${B}_{\mathrm{fus}}^{*},{B}_{qf}$), as well as complete fusion probability estimated by statistical method within the framework of the dinuclear system model. The difference among complete fusion probabilities calculated by the dinuclear system model for different entrance channels can be explained by the hindrance to complete fusion due to the larger inner fusion barrier ${B}_{\mathrm{fus}}^{*}$ for the transformation of the dinuclear system into a compound nucleus and the increase of the quasifission contribution due to the decreasing of the emission barrier ${B}_{qf}$ of quasifission as a function of the angular momentum. Although these reactions with different entrance channels populate the same compound nucleus $^{216}\mathrm{Ra}$ at similar excitation energies, the model predicts the negligible quasifission probability for reactions having higher entrance channel mass asymmetry and the dominant decay channel is complete fission. For reactions induced by massive projectiles such as $\mathrm{Si}$ and $\mathrm{Ca}$ having lower entrance channel mass asymmetry, the quasifission component is dominant in the evolution of dinuclear system, and the fusion process is extremely hindered.