  Coherent pi0 photo- and electroproduction on 4He and 12C nuclei is
investigated in the framework of a distorted wave impulse approximation in
momentum space. The elementary process is described by the recently developed
unitary isobar model. Medium effects are considered by introducing a
phenomenological Delta self-energy. The recent experimental data for 4He and
12C can be well described over a wide range of energies and emission angles by
the assumption that the Delta-nuclear interaction saturates.
