Study of α-Induced Non-Equilibrium Reactions with Particle-γ Coincidences

Proton spectra have been measured for individual channels of the 209Bi (α, pxn) reaction at beam energies of 45 and 75 MeV using p-γ coincidence techniques. Each reaction channel is characterized by a pronounced and well separated proton peak. For the (α, p) channel, e.g., the peak energies are 26.5 and 55.4 MeV for beam energies of 45 and 75 MeV, respectively. At a beam energy of 75 MeV the proton spectra have additional low-energy tails for the (α, p2n) and (α, p3n) channels. The angular distributions of the protons for the different channels as measured at a beam energy of 45 MeV are strongly forward peaked. For the peak regions the protons carry away almost all available excitation energy and the neutrons are evaporated. The energies of the protons can be understood in the framework of the yrast picture, as discussed in the paper, considering that they populate the entry line. Protons of the observed high energies may be produced by the coupling of the relative motion with the Fermi motion. A comparison with the PEP model is given.