BARRIER AND INTERNAL WAVE CONTRIBUTIONS TO THE QUANTUM PROBABILITY DENSITY AND FLUX IN LIGHT HEAVY-ION ELASTIC-SCATTERING

We investigate the properties of the optical model wave function for l ight heavy-ion systems where absorption is incomplete, such as alpha+C a-40 and alpha+O-16 around 30 MeV incident energy. Strong focusing eff ects are predicted to occur well inside the nucleus where the probabil ity density can reach values much higher than that of the incident wav e. This focusing is shown to be correlated with the presence at back a ngles of a strong enhancement in the elastic cross section, the so-cal led ALAS (anomalous large angle scattering) phenomenon; this is substa ntiated by calculations of the quantum probability flux and of classic al trajectories. To clarify this mechanism, we decompose the scatterin g wave function and the associated probability Bur into their barrier and internal wave contributions within a fully quantal calculation. Fi nally, a calculation of the divergence of the quantum flux shows that when absorption is incomplete, the focal region gives a sizable contri bution to nonelastic processes.