Study of the preequilibrium mechanism for individual channels of the 159Tb, 209Bi(α, charged particle xnγ) reactions with particle-γ coincidences

Abstract The mechanism of preequilibrium emission of protons, deuterons and tritons has been studied for α-induced reactions on 159 Tb and 209 Bi using particle-γ coincidence techniques. The experiments were carried out for α energies of 45, 75 and 110 MeV and the charged ejectiles were detected at angles of 45°, 90° and 135° with respect to the beam direction. The experimental technique allowed to identify individual reaction channels and to determine their differential cross sections as a function of the ejectile energy. The most important finding is that the cross sections of the individual reaction channels show pronounced peaks and additionally low-energy tails for higher beam energies. The peaks are related to the emission of a charged particle in the preequilibrium phase followed by neutron evaporation indicating a breakup-fusion mechanism. For the tails at least two fast particles are emitted resulting from a breakup-fusion mechanism with three or more particles in the continuum. The data furthermore contain information about the depopulation mechanism and it was found that the entry point for compound nucleus decay moves away from the yrast line with increasing beam energy.