Production of heavy residues in nuclear collisions leading to Zp + Zt ⩾ 75 at bombarding energies of E/ A = (11.4–15.3) MeV/u

Abstract

Heavy residues, produced in 40Ar, 84Kr and 86Kr induced reactions at E/ A = 14.5 MeV/u, E/ A = 11.6 MeV/u and E/ A = 11A MeV/u, respectively, have been separated from the projectile beam by the velocity filter SHIP and identified by means of α-spectroscopy. The observed reaction products were assigned to evaporation residues from compound or compound-like nuclei up to Z = 96 rather than from products from deep-inelastic processes. This interpretation is based on the velocity distributions, which peak close to ν CN, the independence of the residue mass distributions from the entrance channel, and from comparisons of the observed mass distributions with results from statistical model calculations. The observed residue cross sections were found to be in the same order as or even higher than the values obtained at bombarding energies close to the fusion barrier. This we regard as a confirmation that fission is a process of low probability at high excitation energies. An analysis of the velocity distributions of the evaporation residues showed that particle emission from a thermally equilibrated compound nucleus dominates; contributions from preequilibrium emission are small.