Excitation energy dependence of fragment-mass distributions from fission of Hg-180,Hg-190 formed in fusion reactions of Ar-36+Sm-144,Sm-154

摘要

Mass distributions of fission fragments from the compound nuclei Hg-180 and Hg-190 formed in fusion reactions Ar-36 + Sm-144 and Ar-36 + Sm-154, respectively, were measured at initial excitation energies of E*(Hg-180) = 33-66MeV and E*(Hg-190) = 48-71MeV. In the fission of Hg-180, the mass spectra were well reproduced by assuming only an asymmetric-mass division, with most probable light and heavy fragment masses (A) over bar (L)/(A) over bar (H) = 79/101. The mass asymmetry for 180Hg agrees well with that obtained in the low-energy beta(+)/EC-delayed fission of Tl-180, from our earlier ISOLDE(CERN) experiment. Fission of 190Hg is found to proceed in a similar way, delivering the mass asymmetry of (A) over bar (L)/(A) over bar (H) = 83/107, throughout the measured excitation energy range. The persistence as a function of excitation energy of the mass-asymmetric fission for both proton-rich Hg isotopes gives strong evidence for the survival of microscopic effects up to effective excitation energies of compound nuclei as high as 40MeV. This behavior is different from fission of actinide nuclei and heavier mercury isotope Hg-198. (C) 2015 The Authors. Published by Elsevier B.V.