The two 3H+4He and 3He+4He fusion reactions at low energies are usually viewed as an approximate external capture process. We study the 4He(3H,γ)7 Li and 4He(3He,γ)7 Be reactions in a cluster model, which can take into account two- and three-body electromagnetic currents, using minimal substitution in the explicit momentum dependence of the two- and three-cluster interactions. Our main goal is to explore how the cross section of the low-energy 3H+4He or 3He+4He capture reactions depends on energy. The astrophysical S-factors for these reactions are calculated at very low energies. We construct the conserved realistic Argonne v18 for two nucleons and Urbana IX or Tucson-Melbourne three-cluster interactions, which are considered for calculation. We also calculate the binding energies and the structural properties of 3H+4He or 3He+4He systems. The binding energies are found to be −37.72 (−36.32) MeV and −39.35 (−37.43) MeV, with (without) three-body interactions for 7Be and 7Li, in satisfactory agreement with other theoretical results and experimental data, respectively.
