Direct study of the α -nucleus optical potential at astrophysical energies using the Zn 64 (p,α) Cu 61 reaction

In the model calculations of heavy element nucleosynthesis processes the nuclear reaction rates are taken from statistical model calculations which utilize various nuclear input parameters. It is found that in the case of reactions involving α particles the calculations bear a high uncertainty owing to the largely unknown low-energy α-nucleus optical potential. Experiments are typically restricted to higher energies and therefore no direct astrophysical consequences can be drawn. In the present work a (p,α) reaction is used for the first time to study the α-nucleus optical potential. The measured 64Zn(p,α)61Cu cross section is uniquely sensitive to the α-nucleus potential and the measurement covers the whole astrophysically relevant energy range. By the comparison to model calculations, direct evidence is provided for the incorrectness of global optical potentials used in astrophysical models.