The elastic scattering of 6Li+28Si at near-barrier energies, Phys

Abstract The 6 Li + 28 Si elastic scattering was studied at near-barrier energies with the aim to probe the threshold anomaly. Angular distributions were measured over a wide angular range (θ lab = 25 • to 150 • ) at 4 energies, namely, 7.5, 9, 11 and 13 MeV. The present data together with previous ones at higher energies, as well as elastic scattering data of 6 Li on various targets at near barrier energies, were analyzed by using optical potentials obtained in a double-folding framework. It was found that the strength of the real part of the potential remains almost independent of energy down to, and possible even below, barrier, while the strength of the imaginary part presents an increase at near barrier energies. The results are discussed. 2003 Elsevier Science B.V. All rights reserved. PACS: 25.70.Bc; 24.10.Ht; 27.20.+n Keywords: Elastic scattering 28 Si( 6 Li, 6 Li); Measured σ (θ ); Double-folding potentials; Deduced optical model parameters; Threshold anomaly; Weakly bound nuclei; Sub-barrier fusion When studying elastic scattering between two stable ions at energies well above the Coulomb barrier, it is adequate to ignore specific effects due to couplings to other reaction channels. It is then plausible to describe scattering by phenomenological or folding potentials which vary slowly with energy. This picture no longer remains valid when approaching the vicinity of E-mail address: apakou@cc.uoi.gr (A. Pakou). the Coulomb barrier. Couplings between various channels increase in importance and in describing elastic scattering, either these couplings have to be taken into account through coupled channel theories, or the energy dependence of the various optical model parameters has to be considered explicitly. In fact, the term "threshold anomaly" was invoked to describe a rapid variation of such model parameters around the barrier. This variation is visualized as a localized peak in the strength of the real potential, associated with a sharp 0370-2693/03/$ -see front matte