Cross section of $\alpha$-induced reactions on iridium isotopes obtained from thick target yield measurement for the astrophysical $\gamma$ process

Abstract

The stellar reaction rates of radiative $\alpha$-capture reactions on heavy isotopes are of crucial importance for the $\gamma$ process network calculations. These rates are usually derived from statistical model calculations, which need to be validated, but the experimental database is very scarce. This paper presents the results of $\alpha$-induced reaction cross section measurements on iridium isotopes carried out at first close to the astrophysically relevant energy region. Thick target yields of ${}^{191}$Ir($\alpha$,$\gamma$)${}^{195}$Au, ${}^{191}$Ir($\alpha$,n)${}^{194}$Au, ${}^{193}$Ir($\alpha$,n)${}^{196m}$Au, ${}^{193}$Ir($\alpha$,n)${}^{196}$Au reactions have been measured with the activation technique between E${}_{\alpha }=13.4$ MeV and 17 MeV. For the first time the thick target yield was determined with X-ray counting. This led to a previously unprecedented sensitivity. From the measured thick target yields, reaction cross sections are derived and compared with statistical model calculations. The recently suggested energy-dependent modification of the $\alpha$+nucleus optical potential gives a good description of the experimental data.

Accepted for publication in Physics Letters B

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• Role of consistent parameter sets in an assessment of the alpha-particle optical potential below the Coulomb barrier