Isospin conservation in preequilibrium reactions

Abstract

Previous studies of the extent of isospin mixing in preequilibrium reactions in the continuum have concentrated on reactions with nucleons in both the entrance and exit channels and with incident energies of 30 MeV or less. Using an expanded database for light-particle reactions that includes complex particle channels and higher incident energies, a new investigation of preequilibrium and, at the lower incident energies, equilibrium mechanisms has been carried out. Although many of the measured inclusive energy spectra are insensitive to whether isospin is assumed to be mixed or conserved during the reaction, other spectra reveal evidence that isospin is conserved during the preequilibrium phase of a reaction when the excitation energy in the intermediate nucleus is less than four times the symmetry energy. When isospin is conserved during energy equilibration, good agreement with experiment is typically obtained when the corresponding amount of isospin conservation at equilibrium is taken to be around 40%, though this number is model dependent.