Boltzmann master equation analysis of preequilibrium neutron emission from heavy-ion collisions at 35 MeV/nucleon.

Abstract

The Boltzmann master equation model was used to study preequilibrium neutrons emitted in coincidence with light fragments from collisions of $^{14}$N${+}^{165}$Ho at 35 MeV/nucleon. The input parameters of the model were adopted from earlier analyses of neutron spectra gated by evaporation residues at similar and somewhat lower incident energies. Both the shapes and the absolute magnitudes of the spectra of neutrons in coincidence with light fragments could be reproduced, provided a reduced excitation energy was used in the calculations. The energy removed from the excitation energy was equated with the collective energy of the intermediate state dinuclear complex. For collisions leading to high-energy fragments near the grazing angle, this collective energy corresponds to the kinetic energies above the Coulomb barrier of the projectilelike and targetlike fragments in the center-of-mass system, assuming a binary reaction. For more strongly damped collisions, the spin rotational energies of the fragments was also included. This is qualitatively in agreement with a binary reaction where the energy held in collective modes of the intermediate state is unavailable for preequilibrium emission processes.