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

Abstract

Cross sections of ${}^{120}$Sn($\alpha$,$\alpha$)${}^{120}$Sn elastic scattering have been extracted from the $\alpha$ particle beam contamination of a recent ${}^{120}$Sn(${}^6$He,${}^6$He)${}^{120}$Sn 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 ${}^{120}$Sn(${}^6$He,${}^6$He)${}^{120}$Sn data may be used as the basis for the construction of a simple global ${}^6$He optical potential. The comparison of the ${}^6$He and $\alpha$ data shows that the halo nature of the ${}^6$He nucleus leads to a clear signature in the reflexion coefficients ${\eta }_L$: the relevant angular momenta $L$ with ${\eta }_L\gg 0$ and ${\eta }_L\ll 1$ are shifted to larger $L$ with a broader distribution. This signature is not present in the $\alpha$ scattering data and can thus be used as a new criterion for the definition of a halo nucleus.

Comments: 13 pages, 7 figures, accepted for publication in Phys. Rev. C