Charged-particle evaporation and pre-equilibrium emission in 1.2 GeV proton-induced spallation reactions

Absolute cross sections, energy spectra, and angular distributions have been measured for 1,2,3H, 3,4,6He, 6,7,8,9Li and 7,9,10Be isotopes produced in 1.2 GeV proton-induced spallation reactions with targets between Al and Th. Results of simulation calculations with the intra-nuclear cascade code INCL2.0 coupled to the statistical model GEMINI are in good agreement with these data, as to charged-particle evaporation, mean excitation energy, and mean linear momentum transfer. The pre-equilibrium emission of composite particles, not accounted for in these simulations, however, typically contributes to the total production of composite particles by 40–60% for 2H and 3He, 20–40% for 3H, 5–20% for 4He, and about 15–25% for Li and Be. The composite pre-equilibrium particles together carry off a mean energy of up to 50 MeV, i.e., about 30% compared to the mean energy released by particle evaporation. For deuterons, pre-equilibrium emission is shown to be well described by surface coalescence while definitely other mechanisms are required for 4He and heavier clusters.