Proton Emission in Pre-Equilibrium Reactions Induced by Incident Protons of 100 TO 200 Mev.

Pre-equilibrium reactions induced by medium-energy light ions have become of increasing importance in recent years as they represent the bulk of the measured spectrum. On a nuclear time scale these reactions take place after a one-step process of exciting discrete states in the residual nucleus but long before the process whereby the projectile distributes its kinetic energy equally over all target nucleons to form a compound nucleus which decays statistically. Most existing semi-classical and quantum mechanical models describe the emission of pre-equilibrium particles in terms of a sequence of nucleon-nucleon interactions inside the target nucleus from which particles can be emitted after any stage. The present study was initiated to address discrepant interpretations on the assumed role of a knockout mechanism, leading to two-particle emission after the first step in the reaction of protons with medium to heavy target nuclei, at incident energies above 100 MeV. In an attempt to resolve these discrepancies, inclusive continuum spectra measured at incident energies between 100 and 200 MeV, are analysed in terms of a quasifree scattering mechanism as part of the first step in a multistep process. The dominant feature of a quasifree doorway process in the decay of the continuum is further emphasised by the supplementary data of the coincidence ^{197}Au(p,2p) measurement at 200 MeV. Hence this study has shown that the energy region between 100 and 200 MeV encompasses a probable transition from the dominance of multistep processes to the increasing importance of quasifree scattering in pre-equilibrium reactions.