Systematic behavior of mass distributions in48Ti-induced fission at near-barrier energies

The mass distributions of the fission fragments were measured in reactions induced by ${}^{48}$Ti beams on ${}^{144,154}$Sm, ${}^{162}$Dy, ${}^{174}$Yb, ${}^{186}$W, ${}^{192}$Os, ${}^{196}$Pt, ${}^{200}$Hg, and ${}^{208}$Pb targets at near-barrier energies. The systematic tendencies of the mass widths have been explored. For the reactions with the lighter or spherical target nuclei, the mass widths increase with increasing bombarding energy, a behavior expected for fusion-fission. For the heavier and statically deformed nuclei, the mass widths increase rapidly as energies fall close to and below the capture barriers. Well above the barrier energies, the mass widths and estimated minimum quasifission contributions increase smoothly with increasing fissility of the composite nucleus. The observed behavior is a complex function of the fissility, deformation, and energy with respect to the capture barrier. Comparisons with dynamical quasifission model calculations for these reactions will be a good test of models of fusion in heavy-element formation reactions.