Nuclear structure dependence of fusion hindrance in heavy element synthesis

Abstract

The production of the heaviest elements in fusion-evaporation reactions is substantially limited by very low cross sections, as fusion cross sections (including fusion-fission) are greatly reduced by the competing quasifission mechanism. Using the Australian National University Heavy Ion Accelerator Facility and CUBE detector array, fission fragments from the $^{48}\mathrm{Ti}+^{204,208}\mathrm{Pb}$ and $^{50}\mathrm{Ti}+^{206,208}\mathrm{Pb}$ reactions have been measured, with the aim to investigate how the competition between quasifission and fusion-fission evolves with small changes in entrance-channel properties associated mainly with the nuclear structure. Analysis of mass-distribution widths of strongly mass-angle-correlated fission fragments within the framework of the compound-nucleus fission theory demonstrates significant differences in quasifission (and therefore fusion) probabilities among the four reactions. The impact of nuclear structure on fusion highlights the importance of future radioactive beams.