Abstract
Both 13C 16O and 22Ne 25Mg reactions perform a cosmic role in the production of neutrons in AGB stars, which significantly contributes to the nucleosynthesis via the s-process. The astrophysical S-factor for both reactions has been calculated in this research, utilizing EMPIRE code and depending on two parameter sets for the optical potential: McFadden and Satchler (MFS), and Avrigeanu and Hodgson (AH) for the non-resonant region of the spectrum, and over a temperature range . The extrapolated S-factor at zero energy is derived to be and for 13C 16O, and for 22Ne 25Mg from using MFS and AH parameter sets respectively, and they show a reasonable agreement with the most recommended value. The differences in the S-factor, S(E), values obtained from these two adopted parameters set, were attributed to the variations of the real potential term's diffuseness parameter that affecting the reaction cross section, hence S-factor, and specifically at low energy region. Moreover, the present results imply an influential enhancement of the rates by the electron shielding effect at the low-temperature region in which 13C 16O reaction activated, and especially on 22Ne 25Mg reaction. In addition, for both adopted reactions and overall selected temperature range, the reaction rates using values based on MFS showed acceptable results with other previous compilations and reference libraries. While that obtained from AH exceed all other compilations even though the resonance contributions are currently unconsidered.
Highlights
Asymptotic Giant Branch (AGB) represents an important stage of stellar phases that supplement the universe with elements heavier than iron
In this work, the thermonuclear reaction rates of these reactions will be studied, through investigating the impact of the spherical optical model potential on the cross-section calculations based on the Hauser-Feshbach (HF) model, and the S-factor
At stellar conditions where the excitation energies of the incident particles are frequently low, the nuclear reactions are dominated by compound nucleus (CN) reaction, in which the reaction mechanism is accomplished by the CN formation followed by its decay on a time scale of about or more [11]
Summary
Asymptotic Giant Branch (AGB) represents an important stage of stellar phases that supplement the universe with elements heavier than iron. They all confirmed that two neutron donor reactions mainly supply the s-process with the necessary neutron fluxes in this type of stars, 13C(α, n)16O and 22Ne(α,n)25Mg, with a major and minor contributions from the former and the latter reaction, respectively [2] Despite their low Gamow windows, their influence in elements synthesis up to 209Bi, in addition to their contribution in the production of about half of the heavy nuclei of the universe, made the13C(α, n)16O and 22Ne(α,n)25Mg reactions attract great attention in many astrophysical studies [2,3,4]. Malta nuclear reaction model code [5] with two spherical optical models parameter sets from MFS [6], and AH [7] These were used for determining the parameter, the Modified Lorentzian model for gamma strength function, width fluctuation correction based on Hofmann, Richert, Tepel, and Weidenmuller (HRTW) model, and Gilbert-Cameron model for level density calculations. Input parameters were executed from the Reference Input Parameters Library (RIPL-3) database
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