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

TL;DR

This study measures alpha-induced reaction cross sections on iridium isotopes near astrophysical energies, validating statistical models crucial for understanding the gamma process in stellar nucleosynthesis.

Contribution

First experimental measurement of iridium isotope reaction cross sections at astrophysically relevant energies using thick target yields and X-ray counting, providing validation for statistical models.

Findings

Reaction cross sections agree with modified optical potential models.

Thick target yield measurement with X-ray counting enhances sensitivity.

Data supports the use of energy-dependent optical potentials in models.

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.