  We study inelastic scattering of energetic electrons off a Kondo impurity. If
the energy E of the incoming electron (measured from the Fermi level) exceeds
significantly the Kondo temperature T_K, then the differential inelastic
cross-section \sigma (E,w), i.e., the cross-section characterizing scattering
of an electron with a given energy transfer w, is well-defined. We show that
\sigma (E,w) factorizes into two parts. The E-dependence of \sigma (E,w) is
logarithmically weak and is due to the Kondo renormalization of the effective
coupling. We are able to relate the w-dependence to the spin-spin correlation
function of the magnetic impurity. Using this relation, we demonstrate that in
the absence of magnetic field the dynamics of the impurity spin causes the
electron scattering to be inelastic at any temperature. Quenching of the spin
dynamics by an applied magnetic field results in a finite elastic component of
the electron scattering cross-section. The differential scattering
cross-section may be extracted from the measurements of relaxation of hot
electrons injected in conductors containing localized spins.

Strongly Correlated Electrons