Direct and compound-nucleus reaction mechanisms in theBe7+Ni58system at near-barrier energies

The energy and angular distributions of He-3 and He-4 ions produced in the Be-7 + Ni-58 reaction at a bombarding energy of 22 MeV have been measured for the first time. The yield of the heavier helium isotope was four to five times more abundant than that of its lighter counterpart, ruling out the possibility that in this energy range the Be-7 reaction dynamics is dominated by the exclusive breakup process Be-7 -> He-3 + He-4 (S-alpha = 1.586 MeV). Extensive kinematic and theoretical calculations suggest that the He-3 ions mostly originate from the He-4-stripping process and the He-4 production is mainly triggered by the fusion-evaporation channel. The role played by the breakup, He-3-stripping, 1n-stripping, and 1n-pickup processes is also discussed.