Low-energyR-matrix fits for theLi6(d,α)He

Abstract

Background:The information about the 6 Li(d, α) 4 He reaction rates of astrophysical interest can be obtained by extrapolating direct data to lower energies, or by indirect methods. The indirect Trojan horse method, as well as various R-matrix and polynomial fits to direct data, estimate the electron screening energies much larger than the adiabatic limit. Calculations that include the subthreshold resonance estimate smaller screening energies.Purpose: Obtain the 6 Li(d, α) 4 He reaction R-matrix parameters and the bare astrophysical S factor for the energies relevant to the stellar plasmas by fitting the R-matrix formulas for the subthreshold resonances to the S-factor data above 60 keV. Methods:The bare S factor is calculated using the single-and the two-level R-matrix formulas for the closest to the threshold 0 + and 2 + subthreshold states at 22.2, 20.2 and 20.1 MeV. The electron screening potential U e is then obtained by fitting it as a single parameter to the low-energy data. The calculations are also done by fitting U e simultaneously with other parameters.Results: The low-energy S factor is dominated by the 2 + subthreshold resonance at 22.2 MeV. The influence of the other two subthreshold states is small. The resultant electron screening is smaller than the adiabatic value. The fits that neglect the electron screening above 60 keV produce a significantly smaller electron screening potential. The calculations show a large ambiguity associated with a choice of the initial channel radius. Conclusions:The R-matrix fits do not show a significantly larger Ue than predicted by the atomic physics models. The R-matrix best fit provides U e = 149.5 eV and S b (0) = 21.7 MeV b.

ASTROPHYSICAL IMPACT OF THE UPDATED9Be(p,α)6Li AND10B(p,α)7Be REACTION RATES AS DEDUCED BY THM

“…In recent years, THM data allowed for a better understanding of different astrophysical problems, such as the study of light element burning reactions (Pizzone et al 2005(Pizzone et al , 2014Lamia et al 2008Lamia et al , 2012bLamia et al , 2012cLamia et al , 2013Tumino et al 2011aTumino et al , 2011bTumino et al , 2014Grineviciute et al 2015), CNO reactions (see La Cognata et al 2010Sergi et al 2010;Palmerini et al 2013), and removing/producing neutron reactions (Lamia et al 2008;Gulino et al 2010Gulino et al , 2013La Cognata et al 2012). …”

Nuclear fusion induced by x rays in a crystal

“…The authors of Ref. [10] also showed that this resonance predominantly decays into the αα-channel. They found that the partial width for such a decay is Γ α = 0.77 MeV, which gives Γ α /Γ ≈ 0.96.…”

“…Recent analysis of experimental data, based on the R-matrix parametrization [10], showed that at the near-threshold energies the inelastic collision of d and 6 Li mainly leads to formation of that resonance 8 Be * (2 + , 0, 22.2 MeV). The authors of Ref.…”

Measurement of astrophysical S-factor for 9Be(d, α 0)7Li and 9Be(d, α 1)7Li* reactions at low energies *

“…Besides, the accurate measurement of these reactions in the low energy region may be used to test the nuclear reaction theory that may provide insights into the influence of the Oppenheimer effect [4] and electron screening effect [5] on the cross section at low energies. The analysis of d-T reactions at low energies by R-matrix theory has been proved to be quite successful [6]. This method has been used in deuterium induced reactions on heavier nuclei [7].…”