Range of Validity of the Eikonal Approximation Within the Coupled-channel Description of Heavy-ion Scattering Processes

The validity of the eikonal approximation in heavy-ion reactions is systematically investigated for both potential scattering and coupled-channel processes. Simple prescriptions are advanced to account for Coulomb and nuclear distortions of the trajectory within the eikonal description. The strong nuclear absorption characterizing heavy-ion collision favours the extension of the limit of validity of the eikonal approximation to larger angles and to lower energies than probably expected, i.e. of the order of 30-40 MeV per nucleon in the case of elastic scattering or inelastic processes with very low excitation energies. In the case of inelastic excitation to high-lying modes, and in particular at the lowest bombarding energies, the agreement between the eikonal predictions and the exact ones is worsened by the finite Q-values, but not invalidated if proper corrections for the momentum-mismatch are accounted for. A similar argument also applies to the strong-coupling situations, where the discrepancies are amplified by the multistep nature of the process.