Dominance of fission-fragment proton shells in the mass-asymmetric fission of Pt 176,186 following S 32 + Sm 144,154 fusion

The observation of mass-asymmetric fission in the neutron-deficient sublead region has dramatically expanded the region of mass-asymmetric fission in the nuclide chart, and has led to intense experimental and theoretical investigations. The mechanism for this asymmetric fission mode in this mass region is still not fully understood. To investigate the systematic evolution of the mass-asymmetric fission modes with increasing excitation energy and varying neutron numbers of the neutron-deficient nuclei, the fission-fragment mass distributions have been measured in fissions of the excited compound nuclei Pt176,186 formed by fusion of S32+Sm144,154 over a wide excitation energy range. The fission-fragment mass distributions of Pt176,186 can be described by two main fission modes at all the measured energies, that is one mass-symmetric and one mass-asymmetric fission based on triple-Gaussian fits. In addition, the gef model was used to provide a general prediction for the present paper. The available experimental systematics for the fission of neutron-deficient Pt isotopes suggests that the proton shell of the fragments dominates the mass-asymmetric fission mode, with the most probable proton number being ZL≈35 for the light fragments and ZH≈43 for the heavy ones.