  Relaxation of conduction electron spins in a semiconductor owing to the
hyperfine interaction with spin-1/2 nuclei, in zero applied magnetic field, is
investigated. We calculate the electron spin relaxation time scales, in order
to evaluate the importance of this relaxation mechanism. Master equations for
the electron spin density matrix are derived and solved. Polarized nuclear
spins can be used to polarize the electrons in spintronic devices.
