REMARKABLE OPTICAL-POTENTIAL SYSTEMATICS FOR LIGHTER HEAVY-IONS

Nuclear rainbows, which appear in the elastic scattering angular distr ibutions for certain combinations of Lighter heavy ions like C-12+C-12 and O-16+O-16, uniquely determine the major features of the optical p otentials for these systems. These features are conveniently summarize d by the central depth of the real part of the potential, V(r=0)simila r to 100-300 MeV, and by the ratio of imaginary to real parts of the p otential, W(r)/V(r), found to be much less than 1 for both small and l arge r (internal and far-tail transparency), but approximate to 1 in t he surface region. The resulting maximum in W/V, which is found over t he entire energy range 6 MeV less than or similar to E(L)/A less than or similar to 100 MeV, appears to correlate with the peripheral reacti ons that occur in this energy range. At higher energies the data avail able indicate that the far-surface region is no longer transparent. Ra ther, W approximate to V there, suggesting the dominance of nuclear kn ockout reactions in the far tail. The knockout mode of inelasticity is the one described by the double-Glauber approximation, and W(r)approx imate to V(r) agrees with the Glauber prediction in the high-energy ra nge. This suggests that the double-Glauber prediction begins to be acc urate in the low-density tail of the A(1)+A(2) interaction around E(L) /A approximate to 100 MeV and that its failure for the higher-density interior may provide a means of investigating the density dependence o f Pauli blocking on NN scattering in the nuclear medium. By way of con trast, systems like Ne-20+C-12 and N-14+C-12, which do not exhibit rai nbows, have distinctly more absorptive potentials and do not follow th e above systematics. This suggests that the imaginary part of the opti cal potential reflects the shell structure of the target and/or projec tile in important ways, and so will not be easy to calculate from an i nfinite-matter many-body approach.