Evolution of signatures of quasifission in reactions forming curium

Abstract

Background: Quasifission, a fission-like reaction outcome in which no compound nucleus forms, is an important competitor to fusion in reactions leading to superheavy elements. The precise mechanisms driving the competition between quasifission and fusion are not well understood.Purpose: To understand the influence reaction parameters have on quasifission probabilities, an investigation into the evolution of quasifission signatures as a function of entrance channel parameters is required.Methods: Using the Australian National University's (ANU) CUBE detector for two-body fission studies, measurements were made for a wide range of reactions forming isotopes of curium. Important quasifission signatures---namely, mass-ratio spectra, mass-angle distributions, and angular anisotropies---were extracted.Results: Evidence of quasifission was observed in all reactions, even for those using the lightest projectile (${}^{12}\text{C}+{}^{232}\text{Th}$). But the observables showing evidence of quasifission were not the same for all reactions. In all cases, mass distributions provided some evidence of the possible presence of quasifission but were not sufficient in most cases to clearly identify reactions for which quasifission was important. For reactions using light projectiles (${}^{12}$C, ${}^{28,30}$Si, ${}^{32}$S), experimental angular anisotropies provided the clearest signature of quasifission. For reactions using heavier projectiles (${}^{48}$Ti, ${}^{64}$Ni), the presence of mass-angle correlations in the mass-angle distributions provided strong evidence of quasifission and also provided information about quasifission timescales.Conclusions: The observable offering the clearest signature of quasifission differs depending on the reaction timescale.