Preequilibrium neutron emission in deep-inelastic collisions of 86Kr on 166Er at 11.9 MeV/nucleon

Neutrons emitted in the deep inelastic collisions of ⁸⁶Kr on ¹⁶⁶Er at 11.9 MeV/nucleon, were measured in coincidence with both fragments. The velocity and angular distributions of the neutrons cannot be accounted for by assuming only isotropic evaporation from the fully accelerated fragments. The experimental analysis shows the presence of a preequilibrium component of neutrons emitted mainly on the side of the light fragments in quasielastic events, and on the side of the heavy fragments in strongly damped events. The qualitative features of the data are reproduced by a simple model which assumes that ~ 10% of the neutrons are knocked out at an early stage of the collision along the direction of the nuclear motion. Except for the preequilibrium component the neutron multiplicities are in good agreement with the predictions of evaporation model calculations. NUCLEAR REACTIONS ¹⁶⁶Er(⁸⁶Kr, A_L)A_H, E_lab=1.02 GeV; 35<=A_L<=126, θ_lab=6°-28° E_n, θ_n, φ_n in coincidence with fragments; deduced c.m. neutron energy spectra, neutron multiplicities; evidence for preequilibrium neutron emission.