Inclusive neutron cross sections at forward angles from Nb-Nb and Au-Au collisions at 800 MeV/nucleon.

Abstract

Inclusive neutron spectra were measured at 0\ifmmode^\circ\else\textdegree\fi{}, 4\ifmmode^\circ\else\textdegree\fi{}, 8\ifmmode^\circ\else\textdegree\fi{}, 15\ifmmode^\circ\else\textdegree\fi{}, 30\ifmmode^\circ\else\textdegree\fi{}, and 42\ifmmode^\circ\else\textdegree\fi{} from Nb-Nb and Au-Au collisions at 800 MeV/nucleon. A peak that originates from neutron evaporation from the projectile appears in the spectra at angles out to 8\ifmmode^\circ\else\textdegree\fi{}. The shapes and magnitudes of the spectra are compared with those calculated from models of nucleus-nucleus collisions. The differential cross sections for Au-Au collisions are about four times those for Nb-Nb collisions. The predictions of the Vlasov-Uehling-Uhlenbeck (VUU) and QMD theories agree with the angular distributions of the differential cross sections except at small angles; the VUU prediction overestimates the angular distributions from a few degrees to about 20\ifmmode^\circ\else\textdegree\fi{}, whereas the QMD prediction underestimates the angular distributions below 8\ifmmode^\circ\else\textdegree\fi{}. The Firestreak model overestimates the angular distribution for Nb-Nb collisions and underestimates it for Au-Au collisions. Also, the VUU and QMD models agree with the measured double-differential cross sections in more angular and energy regions than the Firestreak and intranuclear cascade models; however, none of the models can account for the peaks at small angles (\ensuremath{\theta}\ensuremath{\le}15\ifmmode^\circ\else\textdegree\fi{}).