Inclusive mass, energy, and angular distributions of all fragments with $A\ge 6$ have been measured for alpha-particle-induced reactions on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ at five energies between 49 and 159 MeV. From these data the evolution of the dominant reaction mechanisms with energy is characterized. Based on analysis of the mean value of the mass distribution, it appears that linear momentum transfer from projectile to target initially increases with beam energy and reaches a maximum at about 30-40 MeV/nucleon. The low-energy data are consistent with compound nucleus formation and simple transfer processes. At higher energies the growth of forward-peaked angular distributions, continuum energy spectra, and the disappearance of two-body states demonstrate the increasing importance of nucleon-nucleon collisions and multibody breakup mechanisms as the velocity of the projectile exceeds the Fermi velocity. The observed total reaction cross section decreases with increasing bombarding energy. Inclusion of these new data into the excitation functions for $6\le A\le 11$, which are required for nucleosynthesis calculations relevant to the origin of the elements Li, Be, and B, does not significantly alter conclusions based on previously available data.

• Received 22 June 1983

DOI:https://doi.org/10.1103/PhysRevC.29.1595