Background: α-nucleus potentials play an essential role for the calculation of α-induced reaction cross sections at low energies in the statistical model. Uncertainties of these calculations are related to ambiguities in the adjustment of the potential parameters to experimental elastic scattering angular distributions and to the energy dependence of the effective α-nucleus potentials. Purpose: The present work studies the total reaction cross section σ reac of α-induced reactions at low energies which can be determined from the elastic scattering angular distribution or from the sum over the cross sections of all open nonelastic channels. Method: Elastic and inelastic64 Zn(α,α) 64 Zn angular distributions were measured at two energies around the Coulomb barrier, at 12.1 and 16.1 MeV. Reaction cross sections of the (α,γ ), (α,n), and (α,p) reactions were measured at the same energies using the activation technique. The contributions of missing nonelastic channels were estimated from statistical model calculations. Results: The total reaction cross sections from elastic scattering and from the sum of the cross sections over all open nonelastic channels agree well within the uncertainties. This finding confirms the consistency of the experimental data. At the higher energy of 16.1 MeV, the predicted significant contribution of compound-inelastic scattering to the total reaction cross section is confirmed experimentally. As a by-product it is found that most recent global α-nucleus potentials are able to describe the reaction cross sections for 64 Zn around the Coulomb barrier. Conclusions: Total reaction cross sections of α-induced reactions can be well determined from elastic scattering angular distributions. The present study proves experimentally that the total cross section from elastic scattering is identical to the sum of nonelastic reaction cross sections. Thus, the statistical model can reliably be used to distribute the total reaction cross section among the different open channels.

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Background:The γ process in supernova explosions is thought to explain the origin of proton-rich isotopes between Se and Hg, the so-called p nuclei. The majority of the reaction rates for γ process reaction network studies have to be predicted in Hauser-Feshbach statistical model calculations using global optical potential parametrizations. While the nucleon + nucleus optical potential is fairly well known, for the α + nucleus optical potential several different parametrizations exist and large deviations are found between the predictions calculated using different parameter sets. Purpose: By the measurement of elastic α-scattering angular distributions at energies around the Coulomb barrier a comprehensive test for the different global α + nucleus optical potential parameter sets is provided. Methods: Between 20 • and 175 • complete elastic alpha scattering angular distributions were measured on the 113 In p nucleus with high precision at E c.m. = 15.59 and 18.82 MeV. Results: The elastic scattering cross sections of the 113 In(α,α) 113 In reaction were measured for the first time at energies close to the astrophysically relevant energy region. The high precision experimental data were used to evaluate the predictions of the recent global and regional α + nucleus optical potentials. Parameters for a local α + nucleus optical potential were derived from the measured angular distributions. Conclusions: Predictions for the reaction cross sections of 113 In(α, γ ) 117 Sb and 113 In(α,n) 116 Sb at astrophysically relevant energies were given using the global and local optical potential parametrizations.

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