Isospin effects in a covariant transport approach to spallation reactions: Analysis of $p+Fe$ and $Pb$ reactions at 0.8, 1.2 and 1.6 GeV

摘要

We have investigated the influence of different non-linear relativistic meanfield models ($NL$, $NL\rho$ and $NL\rho\delta$) on spallation neutrons forp+Fe and Pb reactions at 0.8, 1.2 and 1.6 GeV by means of a relativisticBoltzmann Uehling Uhlenbeck (RBUU) approach plus a statisticalmultifragmentation (SM) decay model. We find that the "evaporation shoulder",i.e. the neutron energy spectrum from 3 to 30 MeV, almost for any emissionangle is quite sensitive to the isospin part of the mean field. For the moreneutron-rich Pb-target the evaporation component can be directly related to thelow density behavior on the symmetry energy in the thermal expansion phase ofthe excited compound system. It turns out that the spallation data for thereactions under study are shown to be more consistent with RBUU+SM employingthe $NL\rho$ effective lagrangian.