In How A Supernova Explodes, Scientific American, by Bethe and Brown, there is this passage. Wow 10% of the mass equivalent of the neutron star. What an amazing number. But as I see it, the number of neutrinos should equal the number of protons in the pre collapse core material (which should be roughly the same as the number of electrons and the number of neutrons). So an electron and a proton combine, yielding a neutron and a neutrino. In addition those parent particles have lots of kinetic energy at 100 billion degrees. But the neutrino is exceedingly light. 10% of the neutron star's mass equivalent seems like far more energy than these neutrinos can carry away. I must be missing an important factor, either in number of neutrinos or in the energy per neutrino.