Spherical and Deformed Shell Effect Competition in Quasifission of Superheavy Nuclei

Abstract

Quasifission, along with fusion-fission, represent the two most likely reaction outcomes to occur post-capture in collisions leading to superheavy nuclei. As such, understanding these mechanisms and how they relate to one another is key to understanding the intricate dynamics that drive the formation (or dissociation) of the nascent compound nuclei formed in fusion reactions. This understanding directly translates to a more informed picture of suitable reaction partners and can provide vital information for experimental efforts to study the physics and chemistry of superheavy elements. In this work we report results from time-dependent simulations of $^{48}$Ca + $^{238}$U and $^{50}$Ti + $^{236}$Th reactions at incident energies just above the Coulomb barrier with a focus on the quasifission process that prevent the formation of a fully equilibrated $^{286}$Cn compound nucleus. We study these reactions systematically and consider a wide range of initial configurations to extract a robust estimate of primary fragment yields for the quasifission process. Multiple preferred exit channels are observed, with both spherical and deformed shell effects in the heavy and light fragments driving contributions to the production yields depending on the initial configuration of the system. Orientation effects of the deformed actinide targets are found to be a primary driver of which exit channels are populated. Furthermore, the impact of moving away from a doubly-magic projectile is explored with implications towards the reactions considered for current and future superheavy searches.