Quasifission in Kr-84,Kr-86-induced reactions populating superheavy elements

Background: Quasifission plays a detrimental role in the synthesis of superheavy elements. Understanding the dynamics of quasifission helps in selecting the optimum target projectile combinations for the synthesis of new superheavy elements. Purpose: The influence of various entrance channel parameters on the quasifission dynamics was explored. Three reactions, Kr-84 + Pt-198, Kr-86 + Pt-198, and Kr-86 + Au-197, expected to be dominated by quasifission, were studied near the Coulomb barrier energies. Methods: The binary fission fragments from the three reactions were detected using the double arm time-of-flight spectrometer CORSET. The mass and total kinetic energy distributions, which are sensitive to the quasifission dynamics, were measured and analyzed for the three reactions. Results: The mass and total kinetic energy distributions of all the three reactions have the characteristics that show the dominance of quasifission. For the reaction Kr-84 + Pt-198, symmetric quasifission has been found to be relatively more dominant compared to Kr-86 + Pt-198 reaction. The results have been compared with Ca-48- and Cr-52-induced reactions, populating nearby nuclei, to understand the evolution of quasifission. An analysis of the timescales in these reactions using a dynamical calculation shows that Kr-84 + Pt-198 takes a longer time to reach a particular dinuclear shape compared to the other two reactions. The driving potential at the barrier radius also shows a shallower pocket for Kr-84 + Pt-198 compared to Kr-86 + Pt-198 and Kr-86 + Au-197 reactions. Conclusion: The entrance channel isospin difference is found to influence the quasifission dynamics. A higher entrance channel isospin difference may have a larger evolution time, thus driving the systems toward a more symmetric mass split.