  The neutrino driven wind during a core collapse supernova is an attractive
site for r-process nucleosynthesis. The electron fraction $Y_e$ in the wind
depends on observable neutrino energies and luminosities. The mean antineutrino
energy is limited by supernova SN1987A data while lepton number conservation
constrains the ratio of antineutrino to neutrino luminosities. If $Y_e$, in the
wind, is to be suitable for rapid neutron capture nucleosynthesis, then the
mean electron neutrino energy may be significantly lower then that predicted in
present supernova simulations, or there may be new neutrino physics such as
oscillations to sterile neutrinos.
