Effects of alpha-cluster potentials for the O-16+O-16 fusion reaction and S factor

A joint analysis of the elastic-scattering angular distributions and fusion cross sections together with the S factor for the O-16 + O-16 system near and below the Coulomb barrier is reported. To describe these observables within the framework of the optical model, a comparative study of microscopic alpha-alpha double-folding clusters and phenomenological shallow potentials with surface-transparent imaginary parts is performed. Although the phenomenological Woods-Saxon type of shallow real potentials is unable to provide a consistent explanation of these data, the alpha-alpha double-folding cluster potential obtained by considering the alpha-cluster structure of O-16 provides a considerable improvement. The alpha-alpha double-folding cluster potential also reproduces the normalized resonant energy states of S-32 for the N = 24 cluster band.