Evolution of fission and competing decay mechanisms in 40Ar-induced reactions on Au, Th at 27–77 MeV/u of incident energy

Abstract

Fission fragments, heavy reaction residues and the multiplicity of all simultaneously evaporated neutrons are observed from the reactions 40Ar + Au, Th over a wide range of incident 40Ar energy from 27 to 77 MeV/u. The inclusive neutron-multiplicity distributions prove the invariance of energy dissipation with incident energy in these reactions: peripheral collisions with low dissipation and central collisions with high dissipation contribute invariably about half of the reaction cross section. Two fragment correlations and fragment angular distributions show that fission is, for energies in excess of 35 MeV/u, progressively escorted by the emission of lighter complex particles, while the importance of fission generally fades away in favour of very heavy-residue production and, to a smaller extent yet in the considered energy range, eventually also in favour of true multifragmentation.