  We consider the rate of fermion-antifermion pair creation by an external
field. We derive a rate formula that is valid for a coupling with arbitrary
vector and axial vector components to first order in perturbation theory. This
is then applied to study the creation of neutrinos by nuclear matter, a problem
with astrophysical relevance. We present an estimate for the creation rate per
unit volume, compare this to previous results and comment on the role of the
neutrino mass.
