Nuclear and Coulomb contributions to ^6,8He+Si dissociation reactions at low energy

Simple theoretical estimates of the cross sections for 2n removal from ⁶He and for combined 2n and 4n removal from ⁸He are compared with new measurements on Si targets at 0–55 MeV/nucleon. Nuclear effects, described by a microscopic theory of Esbensen and Bertsch, account for nearly all of the observed cross sections. The electric dipole response function for ⁶He obtained by Danilin et al., whose calculations include valence n-n correlations, is used to predict a Coulomb dissociation cross section about 10% as large as that for nuclear dissociation. A smaller upper limit for ⁸He Coulomb dissociation is found by applying the non-energy-weighted sum rule. Equally good fits to the 800-MeV/nucleon ^6,8He+C fragmentation data are obtained.