Abstract
The stellar reaction rates of radiative α-capture reactions on heavy isotopes are of crucial importance for the γ 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 α-induced reaction cross section measurements on iridium isotopes carried out at first close to the astrophysically relevant energy region. Thick target yields of 191Ir(α,γ)195Au, 191Ir(α,n)194Au, 193Ir(α,n)196mAu, 193Ir(α,n)196Au reactions have been measured with the activation technique between Eα=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 α+nucleus optical potential gives a good description of the experimental data.
Highlights
The majority of nuclides heavier than iron are produced via neutron capture reactions [1,2,3,4]
The network calculations use mostly theoretical reaction rates calculated with the Hauser-Feshbach (H-F) statistical model [9]
Experimental reaction rate information can be obtained by measuring the inverse α-capture reaction cross sections [11,12,13] and applying the principle of detailed balance [14]
Summary
The majority of nuclides heavier than iron are produced via neutron capture reactions [1,2,3,4]. While SNIa remain a promising site for p-nucleus production [6, 7], the ccSN model calculations still show deficiencies in reproducing the observed p-nucleus abundances in some nuclear mass regions [5]. Both sites, may contribute to the galactic p-nucleus content. In the astrophysically relevant energy region [16] the H-F cross section calculations are only sensitive to the α-channel width [17], which is calculated using global α+nucleus optical model potentials. The data were compared to H-F calculations for further constraining the optical model potential
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