  It is shown that the large density fluctuations appearing at the onset of the
first order nuclear liquid-gas phase transition can play an important role in
the supernovae evolution. Due to these fluctuations, the neutrino gas may be
trapped inside a thin layer of matter near the proto-neutron star surface. The
resulting increase of pressure may induce strong particle ejection a few
hundred milliseconds after the bounce of the collapse, contributing to the
revival of the shock wave. The Hartree-Fock+RPA scheme, with a finite-range
nucleon-nucleon effective interaction, is employed to estimate the effects of
the neutrino trapping due to the strong density fluctuations, and to discuss
qualitatively the consequences of the suggested new scenario.
