| Abstract: | Total reaction cross sections for protons on ⁴⁰Ca have been measured at fifteen energies between 10.3 MeV and 21.6 MeV by the beam-attenuation method. The differential elastic cross sections for protons on ⁴⁰Ca have been obtained at fifteen energies between 9.8 MeV and 21.7 MeV. These measurements were made at intervals of 3° between 12° and 30° and at intervals of 5° between 35° and 165° in the laboratory. Total reaction cross sections for protons on carbon have been measured at ten energies between 9.8 MeV and 19.5 MeV. The total reaction cross section for ⁴⁰Ca rises sharply at low energies, reaches a maximum value around 13 MeV, and reaches a minimum around 16 MeV. The rise at the lower energies is a result of the Coulomb barrier. The dip at 16 MeV is probably associated with the (p,n) threshold at 16 MeV. The present differential elastic cross sections and total reaction cross sections for ⁴⁰Ca are compared with predictions of the optical model. The total reaction cross sections for carbon show resonant-like structures in the neighborhood of 10.4 MeV and 13.8 MeV. The structure observed in these total reaction cross sections is related to levels around 11.6 MeV and 14.6 MeV in the compound nucleus, ¹³N. Because of the presence of these sharp resonances in the total reaction cross section, it does not seem reasonable to apply the optical model to ¹²Cat lower energies. |
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