The ¹⁹F(α, p)²²Ne Reaction at Energies of Astrophysical Relevance by Means of the Trojan Horse Method and Its Implications in AGB Stars

Abstract

The main source of 19F in the universe has not yet been clearly identified and this issue represents one of the unanswered questions of stellar modeling. This lack of knowledge can be due to the 19F(α, p)22Ne reaction cross-section that has proven to be difficult at low energies: direct measurements stop only at about ∼660 keV, leaving roughly half of the astrophysical relevant energy region (from 200 keV to 1.1 MeV) explored only by R-matrix calculations. In this work, we applied the Trojan Horse Method to the quasi-free three-body 6Li(19F, p22Ne)d reaction performed at E beam = 6 MeV in order to indirectly study the 19F(α, p)22Ne reaction in the sub-Coulomb energy region. In this way, we obtained the cross-section and the reaction rate in the temperature region of interest for astrophysics and free from electron screening effects. A brief analysis of the impact of the new measured reaction rate in AGB star nucleosynthesis is also presented.

Fluorine Destruction in Stellar Environments

“…Such an enhancement can be seen in Table II, along with temperature and rate values. Since the cross-section of the 19 F(α, p) 22 Ne reaction measured through the THM is up to a factor of 4 larger than that reported in the literature, we believe that these experimental results could crucially affect our knowledge of 19 F nucleosythesis in the most relevant energy region for He-shell burning. Such an analysis will be the subject of a forthcoming paper.…”

“…As regards the 19 F(α, p) 22 Ne we refer to [21,22] for details on measurements and data analysis. Again the astrophysical factor was extracted by means of the THM and used to calculate the reaction An increase in the contribution of the present channel higher up to a factor of 4 (if upper limits are considered) shows up in the region of astrophysical interest between 0.2 × 10 9 K and 0.6 ×10 9 K with respect to the literature [23].…”

“…If the pathways in which 19 F is produced are quite clear, it is now important to describe how it can be destroyed. In AGB stars it can happen with the 19 F(p, α) 16 O or 19 F(α, p) 22 Ne reactions [1,2]. Their relative importance critically depends on the environment: in He-rich environment, such as the convective envelope near the He-shell, the latter prevails.…”

Mixing and Magnetic Fields in Asymptotic Giant Branch Stars in the Framework of FRUITY Models

“…In addition, (n, γ) reaction rates for 61 Ni, 74 Se, 79 Kr, 81 Kr, 83 Kr, 84 Sr, 93 Nb, 94 Nb, 103 Rh, 109 Ag, 119 Sn, 121 Sn, 122 Sb, 125 Te, 129 I, 129 Xe, 142 Pr, 147 Pm, 151 Eu, 152 Eu, 153 Eu, 154 Eu, 158 Gd, 158 Dy, 169 Tm, 171 Tm, 170 Yb, 181 Hf, 181 Ta, 182 Ta, 182 W, 183 W, 189 Os, 192I r, 193 Ir, 193 Pt, 205 Pb, and 210 Bi have been recomputed by using the updated stellar enhancement factor (SEF) from the KADoNiS v0.3 database [60]. The new β-decay rate for 60 Fe is from Rugel et al [61].…”

Fluorine Destruction in Stars Studied via Trojan Horse Method

“…This enhancement of the reaction rate can help understanding fluorine nucleosynthesis in AGB stars since a larger 19 F destruction is expected by additional non-standard mixing processes. As regards the 19 F(α, p) 22 Ne we refer to [23,24] for details on measurements and data analysis. Again the astrophysical factor was extracted by means of the THM and used to calculate the reaction rate.…”