No abstract

Background:The nature of asymmetric fission of preactinides is not yet understood in detail, despite intense experimental and theoretical studies carried out at present. Purpose: The study of asymmetric and symmetric fission of 180,182,183 Hg and 178 Pt nuclei as a function of their excitation energy and isospin. Methods: Mass-energy distributions of fission fragments of 180 Hg, 178 Pt (two protons less than 180 Hg), and 182 Hg (two neutrons more than 180 Hg) formed in the 36 Ar + 144 Sm, 142 Nd, and 40 Ca + 142 Nd reactions were measured at energies near and above the Coulomb barrier. Fission of 183 Hg obtained in the reaction of 40 Ca with 143 Nd was also investigated to see if one extra neutron could lead to dramatic changes in the fission process due to the shape-staggering effect in radii, known in 183 Hg. The measurements were performed with the double-arm time-of-flight spectrometer CORSET. Results: The observed peculiarities in the fission fragment mass-energy distributions for all studied nuclei may be explained by the presence of a symmetric fission mode and three asymmetric fission modes, manifested by the different total kinetic energies and fragment mass splits. The yield of symmetric mode grows with increasing excitation energy of compound nucleus. Conclusions: The investigated properties of asymmetric fission of 180,182,183 Hg and 178 Pt nuclei point out the existence of well-deformed proton shell at Z ≈ 36 and a less deformed proton shell at Z ≈ 46.