α- and neutron-induced reactions on ruthenium isotopes

Abstract

The uncertain origin of the proton rich Mo and Ru isotopes has motivated cross-section measurements of \ensuremath{\alpha}- and neutron-induced reactions. The experiments were performed via the activation technique by irradiating thin layers of natural ruthenium with \ensuremath{\alpha}-particle beams close to the Gamov window of the p process between 7.0 and 10.5 MeV. The cross sections of the reactions ${}^{96}\mathrm{Ru}(\ensuremath{\alpha},\ensuremath{\gamma}),$ ${}^{96}\mathrm{Ru}(\ensuremath{\alpha},n),$ ${}^{96}\mathrm{Ru}(\ensuremath{\alpha},p),$ and ${}^{98}\mathrm{Ru}(\ensuremath{\alpha},n)$ could be determined with uncertainties of typically 10%. On average, these results are about two to three times smaller than recent statistical model predictions. Additional activations in a quasistellar neutron spectrum corresponding to $kT=25\mathrm{keV}$ allowed us to obtain the complementary stellar $(n,\ensuremath{\gamma})$ cross sections for ${}^{96}\mathrm{Ru},$ ${}^{102}\mathrm{Ru},$ and ${}^{104}\mathrm{Ru}.$ In these cases the agreement with model calculations is considerably better.