An optical model analysis of the elastic scattering of ${}_{}{}^{11}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ target nuclei has been performed, for measurements at 620 and 637 MeV laboratory incident energy, respectively. The data are from the group of the University of Notre Dame. It has turned out, in the case of the ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ projectile, that it was necessary to use a real and imaginary surface potential peaked very far outside of the nucleus core, in order to reproduce the elastic scattering angular distribution at very forward angles. The extracted optical model reaction cross section leads to a radius of 3.7 fm for ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ in agreement with what is already known in the literature from interaction cross section measurements. On the contrary, the extracted radius for the ${}_{}{}^{11}{}_{}{}^{}\mathrm{C}$ nucleus is 2.5 fm in this experiment. Furthermore, at this high incident energy, a strong far-side component on ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ is evidenced by a Fuller analysis. This large radius for the ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ nucleus, added to the fact that strong refractive effects are observed in the elastic scattering, is a clear signature of a nuclear halo for the ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ nucleus.

• Received 13 January 1993

DOI:https://doi.org/10.1103/PhysRevC.47.2213