Direct and compound-nucleus reaction mechanisms in the Be 7 + Ni 58 system at near-barrier energies

The energy and angular distributions of He3 and He4 ions produced in the Be7+Ni58 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 Be7 reaction dynamics is dominated by the exclusive breakup process Be7\u21923He+He4 (S\u3b1=1.586 MeV). Extensive kinematic and theoretical calculations suggest that the He3 ions mostly originate from the He4-stripping process and the He4 production is mainly triggered by the fusion-evaporation channel. The role played by the breakup, He3-stripping, 1n-stripping, and 1n-pickup processes is also discussed