  We have measured the ionization efficiency of silicon nuclear recoils with
kinetic energy between 1.8 and 20 keV. We bombarded a silicon-drift diode with
a neutron beam to perform an elastic-scattering experiment. A broad-energy
neutron spectrum was used and the nuclear recoil energy was reconstructed using
a measurement of the time of flight and scattering angle of the scattered
neutron. The overall trend of the results of this work is well described by the
theory of Lindhard et al. above 4 keV of recoil energy. Below this energy, the
presented data shows a deviation from the model. The data indicates a faster
drop than the theory prediction at low energies.
