Astrophysical 3He(α,γ)7Be and 3H(α,γ)7Li direct capture reactions in a potential-model approach

Abstract

The astrophysical 3He(α,γ)7Be and 3H(α,γ)7Li direct capture processes are studied in the framework of the two-body model with potentials of a simple Gaussian form, which describe correctly the phase shifts in the s, p, d, and f waves, as well as the binding energy and the asymptotic normalization constant of the ground p3/2 and the first excited p1/2 bound states. It is shown that the E1transition from the initial s wave to the final p waves is strongly dominant in both capture reactions. On this basis the s-wave potential parameters are adjusted to reproduce the new data of the LUNA Collaboration around 100 keV and the newest data at the Gamov peak estimated with the help of the observed neutrino fluxes from the sun, S34(23+6−5keV)=0.548±0.054 keV b for the astrophysical Sfactor of the capture process 3He(α,γ)7Be. The resulting model describes well the astrophysical Sfactor in the low-energy big-bang nucleosynthesis region of 180–400 keV; however, it has a tendency to underestimate the data above 0.5 MeV. The energy dependence of the S factor is mostly consistent with the data and the results of the no-core shell model with continuum, but substantially different from the fermionic molecular dynamics model predictions. Two-body potentials, adjusted for the properties of the 7Be nucleus, 3He+α elastic scattering data, and the astrophysical S factor of the 3He(α,γ)7Bedirect capture reaction, are able to reproduce the properties of the 7Li nucleus, the binding energies of the ground 3/2− and first excited 1/2− states, and phase shifts of the 3H+α elastic scattering in partial waves. Most importantly, these potential models can successfully describe both absolute value and energy dependence of the existing experimental data for the mirror astrophysical 3H(α,γ)7Licapture reaction without any additional adjustment of the parameters.