Near-Barrier Elastic Scattering of Weakly Bound Nuclei and the Threshold Anomaly

摘要

It is pointed out that the usual threshold anomaly, found operative in the energy behavior of the imaginary and real parts of the optical potential representing the elastic scattering of tightly bound nuclei at near- and below-barrier energies, suffers a drastic qualitative change in the case of the elastic scattering of weakly bound projectile nuclei. Owing to the strong coupling to the breakup channel even at sub-barrier energies, the imaginary potential strength seems to increase as the energy is lowered down to below the natural, barrier, threshold, accompanied by a decrease in the real potential strength. This feature is consistent with the dispersion relation. It also clearly indicates the effective increase of the barrier height. The systems 9Be, 16O + 64Zn and 6,7Li + 138Ba are analyzed to illustrate this new phenomenon.