  The radiative capture cross sections for the 3He(alpha,gamma)7Be and
3H(alpha,gamma)7Li reactions are calculated in the fully microscopic fermionic
molecular dynamics approach using a realistic effective interaction that
reproduces the nucleon-nucleon scattering data. At large distances bound and
scattering states are described by antisymmetrized products of 4He and 3He/3H
ground states. At short distances the many-body Hilbert space is extended with
additional many-body wave functions needed to represent polarized clusters and
shell-model-like configurations. Properties of the bound states are described
well, as are the scattering phase shifts. The calculated S factor for the
3He(alpha,gamma)7Be reaction agrees very well with recent experimental data
both in absolute normalization and energy dependence. In case of the
3H(alpha,gamma)7Li reaction the calculated S factor is larger than available
experimental data by about 15%.
