Electron‐beam‐absorption measurements were performed to investigate the formation and annealing of radiation damage produced by ion implantation into GaP and GaAs0.6P0.4. The fluenceFArequired to yield an amorphous layer, the dependence ofFAon ion mass and target temperature, and the temperatures necessary for annealing were determined. For 140‐keV Ar into GaAs0.6P0.4, we foundFA=1×1014cm−2at 273 K andFA→∞ at 580 K. Our results compare well with known data for GaAs and GaP and demonstrate the applicability of the new method of measurement.