Elastic scattering of 17F, 17O and 19F on a heavy target in microscopic continuum discretized coupled-channels method

Background: Microscopic description of the projectile, based on an effective NN interaction, in a microscopic CDCC (MCDCC) model [PRL 111, 082701 (2013)] has been successfully applied to the 7Li+208Pb scattering. Purpose: The MCDCC method is applied to the low energy elastic scattering of 17F, 17O and 19F on 58Ni and 208Pb targets. The goal of the calculations is twofold - to test the adequacy and the accuracy of the MCDCC model for the heavier projectiles, and to study the contribution of various channels to the elastic scattering cross sections. Methods: The elastic scattering cross sections are calculated using the MCDCC method. The nucleon-target optical potential is folded with the projectile densities resulting from an effective NN interaction, which includes central nuclear, spin-orbit and Coulomb terms. Discretization of the continuum is achieved via the pseudo state method. Coupled equations are solved using the R-matrix method on a Lagrange mesh. Results: For the test case of 17F at 10 MeV/nucleon, the cross sections are weakly sensitive to the choice of the effective NN interaction, three different energy dependent optical nucleon-target potentials provide a similar reasonable agreement with data. Just below the Coulomb barrier, the MCDCC significantly underestimates the cross sections at larger angles. The coupling to continuum is not significant in most of the assessed cases. Conclusions: The MCDCC is very satisfactory in the sense, that it includes the microscopic properties of the projectile in a reaction model. Well above the Coulomb barrier, the cross sections are in a good agreement with data. The reasons for the discrepancy between the data and the calculated cross sections at the lower energies, which is also observed in a traditional CDCC, are unclear

Low-energy R -matrix fits for the Li 6 ( d , α ) He 4 S factor

Background: The information about the 6Li(d,a)4He reaction rates of the astrophysical interest can be obtained by extrapolating direct data to the 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 6Li(d,a)4He reaction R-matrix parameters and the 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 Ue is then obtained by fitting it as a single parameter to the low energy data. 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. R-matrix fits result in the electron screening that is smaller than the adiabatic value. Neglecting the electron screening above 60 keV reduces the electron screening potential significantly. 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 produces Ue=149.5 eV and Sb(0)=21.7 MeV b.Comment: Authors thank the (anonymous) referee for detailed comments and suggestion