Comparison of nonequilibrium processes in p+Ni and p+Au collisions at GeV energies

The energy and angular dependence of double differential cross sections d(2)sigma/d Omega dE were measured for p, d, t, He-3,He-4,He-6, Li-6,Li-7,Li-8, Be-7,Be-9,Be-10, B-10,B-11, and C produced in collisions of 1.2, 1.9, and 2.5 GeV protons with a Ni target. The shape of the spectra and angular distributions almost does not change whereas the absolute value of the cross sections increases by a factor similar to 1.7 for all ejectiles in this beam energy range. It was found that energy and angular dependencies of the cross sections cannot be reproduced by microscopic models of intranuclear cascade including coalescence of nucleons coupled to statistical model for evaporation of particles from excited, equilibrated residual nuclei. The inclusion of nonequilibrium processes, described by a phenomenological model of the emission from fast and hot moving sources, resulting from break up of the target nucleus, leads to very good reproduction of data. Cross sections of these processes are quite large, exhausting approximately half of the total production cross sections. Due to good reproduction of energy and angular dependencies of d(2)sigma/d Omega dE it was possible to determine total production cross sections for all studied ejectiles. Results obtained in this work point to the analogous reaction mechanism for proton induced reactions on Ni target as that observed previously for Au target in the same beam energy range.