HALOS AND RAINBOWS - THE ELASTIC-SCATTERING OF LIGHT EXOTIC NUCLEI

The scattering of an ''exotic'' light nucleus with a ''halo'' is compa red with that of a normal nucleus. Four, sometimes opposing, effects a re identified, arising from the rear and imaginary parts of (i) the ex tended tails of the complex optical potential due to the halo, and (ii ) the complex polarization potential arising from breakup. Semiclassic al expressions are derived which embody the expected differences, and compared with fully quantal optical-model calculations. The cases of L i-11 and C-11 scattering from C-12 at E/A approximate to 60 MeV are ex amined. The net effect of the halo depends upon the details of the int eractions, but we conclude that Li-11 does not exhibit greatly enhance d refraction compared to C-11, and that its elastic scattering cross s ections are similar to, and may be smaller than, those for C-11, in ag reement with preliminary analyses of the measurements.