Competing asymmetric fusion-fission and quasifission in neutron-deficient sub-lead nuclei

To disentangle the role of shell effects and dynamics, fission fragment mass distributions of Au-191, a nucleus in the newly identified island of mass asymmetric fission in the sub-lead region, have been measured down to excitation energy of approximate to 20 MeV above the fission barrier via two different entrance channels, viz. O-16+Lu-175 and Cl-37+(154) Sm reactions. Apart from having signature of the shell effects in both the cases, clear experimental evidence of quasifission has been observed in the mass distributions of the Cl induced reaction, that has also been substantiated by the theoretical calculations. This crucial evidence along with a systematic analysis of the available experimental data has revealed that the dynamics in the entrance channel has significant influence on most of the reactions used earlier to explore the persistence of recently discovered mass asymmetry in beta-delayed fission at low energy in this mass region, ignoring which might lead to ambiguity in interpreting the heavy-ion data. (C) 2020 The Author(s). Published by Elsevier B.V.