  It has been recently proposed that the shocked surface layers of exploding
O-Ne-Mg cores provide the conditions for r-process nucleosynthesis, because
their rapid expansion and high entropies enable heavy r-process isotopes to
form even in an environment with very low initial neutron excess of the matter.
We show here that the most sophisticated available hydrodynamic simulations (in
spherical and axial symmetry) do not support this new r-process scenario
because they fail to provide the necessary conditions of temperature, entropy,
and expansion timescale by significant factors. This suggests that, either the
formation of r-process elements works differently than suggested by Ning et al.
(2007, NQM07), or that some essential core properties with influence on the
explosion dynamics might be different from those predicted by Nomoto's
progenitor model.
