Abstract
Angular distributions and excitation functions for the emission of a large number of proton, deuteron, triton, andα-particle groups in7Li+16O reactions have been measured in the vicinity of the Coulomb barrier. Within the framework of the statistical reaction model, two approaches are presented that can reproduce the only weakly anisotropic shape of the angular distributions and the absolute cross section for those groups of ejectiles where contributions from direct reaction modes are small. When a standard Woods-Saxon potential deduced from elastic scattering is used, the entrance channel angular momentum distribution must be limited to values below critical angular momental cr which are smaller than the grazing angular momental gr if fusion is to be described. A global proximity potential with a parameter set that has been adjusted to reproduce the fusion reactions of a variety of p- and sd-shell nuclei yields very similar results when applied to7Li+16O. The proximity potential effectively introduces a similar angular-momentum limitation. This analysis proves the existence of a fusion cross section limitation and the importance of strong direct reaction modes (transfer and possibly inelastic processes) in7Li+16O reactions at energies close to and even below the Coulomb barrier. Another aspect of7Li+16O is addressed briefly. The resonance-like structure observed in the heavy-ion radiative capture reaction7Li(16O,γ 0+1)23Na atE x (23Na)=25.4 MeV is not observed in the particle decay channels investigated in the present work.
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The authors would like to acknowledge the help received from B. Bellenberg, B. Dechant, H. Hemmert, T. Krischak, E. Kuhlmann, H. Putsch, and C. Scholz during the experiments.