Recoil Study of the ReactionAl27(p, 3pn)Na24

In order to study the mechanism of a simple spallation reaction induced by GeV-energy protons, measurements were made of the momentum properties of ${\mathrm{Na}}^{24}$ nuclei produced from an aluminum target. Data were obtained on: (1) the fraction of ${\mathrm{Na}}^{24}$ nuclei recoiling out of targets thick with respect to the range of the recoils (the targets were oriented both perpendicular and parallel to the proton beam); (2) the distribution of ${\mathrm{Na}}^{24}$ ranges from a thin target measured with plastic catchers subtending an angle of $2\pi$; (3) the angular distribution of the ${\mathrm{Na}}^{24}$ recoils with respect to the beam. Results of Monte Carlo knock-on cascade and evaporation calculations for 0.36- and 1.8-GeV bombarding energies are compared with the data in the laboratory system. The calculations predict sharper sideways peaking in the angular distributions, and more momentum deposition at the higher bombarding energy, than are observed. The experimental data are also reduced to a set of velocity vectors which is then interpreted in terms of a simple, constant-deposition-energy mechanism in which the incident proton makes only one quasi-elastic collision with a single nucleon which does not escape from the nucleus. This treatment accounts for most of the data but also predicts a much larger sideways peaking in the angular distribution than is observed.