Abstract
Background: Information about the 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 -matrix and polynomial fits to direct data, estimate electron screening energies much larger than the adiabatic limit. Calculations that include the subthreshold resonance estimate smaller screening energies.
Purpose: Obtain the reaction -matrix parameters and the bare astrophysical factor for energies relevant to the stellar plasmas by fitting -matrix formulas for the subthreshold resonances to the -factor data above 60 keV.
Methods: The bare factor is calculated using the single- and the two-level -matrix formulas for the closest to the threshold and subthreshold states at , and MeV. The electron screening potential is then obtained by fitting it as a single parameter to the low-energy data. The calculations are also done by fitting simultaneously with other parameters.
Results: The low-energy factor is dominated by the subthreshold resonance at 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 -matrix fits do not show a significantly larger than predicted by the atomic physics models. The -matrix best fit provides eV and MeV b.
- Received 21 April 2013
- Revised 14 October 2014
DOI:https://doi.org/10.1103/PhysRevC.91.014601
©2015 American Physical Society