[en] Surface displacements due to low energy (100-300 eV) Xe ion bombardment of the Ge(001) 2x1 reconstructed surface are investigated by in situ RHEED measurements of surface roughening. The near-exponential decay in RHEED intensity due to displacements of Ge atoms at the surface is shown to depend sensitively on the Xe energy and flux. Iso-damage rate curves at 100 degree C are used to establish a fixed amount of defect annealing and to determine the number of surface displacements per Xe as a function of Xe energy. The calculated number of near-surface displacements per Xe exhibits a similar energy dependence. Comparison of experiment and calculation indicates an efficiency for the production of stable surface defects of about 50% at a temperature of 100 degree C and damage rate of 2x10¹² displacements/cm²-sec. Results indicate this approach will allow the threshold energies for surface atom displacements to be measured. 7 refs., 4 figs