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

TL;DR

This study examines how different relativistic mean field models affect neutron emission spectra in proton-induced spallation reactions on Fe and Pb, highlighting the sensitivity of evaporation neutrons to isospin effects and symmetry energy.

Contribution

It introduces a detailed analysis of isospin effects in spallation reactions using a covariant transport approach with various mean field models, emphasizing the role of the $NL ho$ model.

Findings

Neutron spectra are sensitive to the isospin part of the mean field.

Pb reactions show a link between evaporation neutrons and symmetry energy behavior.

Data favor the $NL ho$ effective Lagrangian model.

Abstract

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