Dynamic effects in fragmentation reactions

Fragmentation reactions offer a useful tool to study the spectroscopy of halo nuclei, but the large extent of the halo wave function makes the reaction theory more difficult. The simple reaction models based on the eikonal approximation for. the nuclear interaction or first-order perturbation theory for the Coulomb interaction have systematic errors that we investigate here, comparing to the predictions of a complete dynamical calculations. We find that stripping probabilities are underpredicted by the eikonal model, leading to extracted spectroscopic strengths that are two large. In contrast, the Coulomb excitation is overpredicted by the simple theory. We attribute this to a screening effect, as is well know in the Barkas effect on stopping powers. The errors decrease with beam energy as E-beam(-1), and are not significant at beam energies above 50 MeV/n. At lower beam energies, the effects should be taken into account when extracting quantitative spectroscopic strengths.