  Measurements of spin dynamics of electrons in a degenerate two dimensional
electron gas, where the Dyakonov-Perel mechanism is dominant, have been used to
investigate the electron scattering time (tp*) as a function of energy near the
Fermi energy. Close to the Fermi energy the spin evolution is oscillatory,
indicating a quasi-collision-free regime of spin dynamics. As the energy is
increased a transition to exponential, collision-dominated, spin decay occurs.
The frequency and the value of tp* are extracted using a Monte Carlo simulation
method. At the Fermi energy tp* is very close to the ensemble momentum
relaxation time (tp) obtained from the electron mobility. For higher energies
tp* falls quadratically, consistent with theoretical expectations for the onset
of electron-electron scattering which is inhibited by the Pauli principle at
the Fermi energy.
