We have measured light-particle energy spectra over a 90° range of angles in the forward hemisphere in coincidence with heavy residues from the reaction ${}_{}{}^{20}{}_{}{}^{}\mathrm{Al}$ at 19.2 MeV/nucleon. A selection on residues with Z≥11 removes the contributions of deep-inelastic scattering and peripheral processes from the fusion-like cross section. With the help of a simple analytic model that includes the coincidence kinematics we are able to describe the data and extract multiplicities, primary-energy distributions, and source velocities for the light particles from fusion-like reactions. The mass difference between the observed fragments and the compound system comes almost exclusively from light particles with Z≤2. The evaporated α particles are more energetic and more numerous than the statistical model implies. The fast α particles have distributions consistent with a fragmentation-fusion picture; however, they account for at most (1/3 of the momentum lost in the incomplete fusion process.

• Received 2 November 1987

DOI:https://doi.org/10.1103/PhysRevC.37.2502