Sources of light particles from fusion-like processes in the 20Ne

Abstract

We have measured light-particle energy spectra over a 90\ifmmode^\circ\else\textdegree\fi{} 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\ensuremath{\ge}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\ensuremath{\le}2. The evaporated \ensuremath{\alpha} particles are more energetic and more numerous than the statistical model implies. The fast \ensuremath{\alpha} 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.