Comparison of 120Sn(6He,6He)120Sn and 120Sn(α,α)120Sn elastic scattering and signatures of the 6He neutron halo in the optical potential

Cross sections of 120Sn(α,α)120Sn elastic scattering have been extracted from the α-particle-beam contamination of a recent 120Sn(6He,6He)120Sn experiment. Both reactions are analyzed using systematic double-folding potentials in the real part and smoothly varying Woods-Saxon potentials in the imaginary part. The potential extracted from the 120Sn(6He,6He)120Sn data may be used as the basis for the construction of a simple global 6He optical potential. The comparison of the 6He and α data shows that the halo nature of the 6He nucleus leads to a clear signature in the reflexion coefficients ηL: The relevant angular momenta L with ηL>>0 and ηL<<1 are shifted to larger L with a broader distribution. This signature is not present in the α-scattering data and can thus be used as a new criterion for the definition of a halo nucleus.