We investigate the condition that the neutrino energies Ev can be considered to be small enough to be neglected in the energy momentum conservation equation the reactions d+ve→u+e- and u+e-→d+ve.It can be simply expressed as Ev＜4αcμe/π,where αc is the strong coupling constant and μe is the electron chemical potential.Then for Ev＜4αcμe/π,we generalize the mean free path for nondegenerate neutrinos given by Iwamoto and obtain aformula that is valid for both nondegenerate and degenerate neutrinos.We also model the mean free path for both nondegenerate and degenerate neutrinos with energies Ev＞4αcμe/π.