Competition between fusion and quasifission in the angular momentum dependent dynamics of heavy element synthesis reactions

Abstract

Background: Mass and angle distribution measurements have illuminated many aspects of the physical variables controlling quasifission. However, mapping from detection angle to reaction time is clouded by the wide range of contributing angular momenta $L\ensuremath{\hbar}$, ranging from $0\ensuremath{\hbar}$ to the maximum of the reaction ($⪆100\ensuremath{\hbar}$), which complicates the mapping, and thus limits our understanding of the reaction dynamics.Purpose: To investigate the angular momentum dependence of the reaction dynamics in quasifission and determine the fission fragment mass evolutions in the reaction.Method: The mass and angular distributions of products of the reactions $^{52}\mathrm{Cr}+^{198}\mathrm{Pt}$ and $^{54}\mathrm{Cr}+^{196}\mathrm{Pt}$ were measured. The distributions were compared with quasifission simulation results.Results: Mass angle distributions are reproduced by utilizing a new quasifission mass evolution model, and including a mass-symmetric component associated with low $L$. The latter increases in yield at higher beam energy.Conclusions: The symmetric component represents the total of slow quasifission and fusion-fission. The increase in contribution with energy above the Coulomb barrier suggests that an extra-push energy is required to achieve fusion.