Systematics of sub- and near-barrier fusion cross sections and the threshold anomaly

Abstract

Systematic behavior observed in the sub- and near-barrier fusion cross sections recently by Stelson et al. reveals a new threshold phenomenon in sub-barrier fusion reactions. We present evidence that the threshold energy mentioned above is approximately equal to another threshold energy extracted from the imaginary part of the optical potential for elastic scattering in the vicinity of the Coulomb barrier. Implications of this agreement are discussed on the basis of the extended optical model. We then show that the main features of the systematics observed in fusion cross sections can also be understood within the framework of this model.