Surfaces of Si(100) irradiated at 110 K with 5 keV He ions under ultrahigh vacuum conditions and subsequently annealed isochronally display abrupt healing of the radiation-induced surface roughness at 160 K. Smoothening also occurs at 160 K for Si(100)-2 x 1 irradiated with 230 eV Ar ions at 110 K, but not for Si(100) following submonolayer Si deposition at 110 K. The data suggest that the smoothening at 160 K following 5 keV He ion irradiation at 110 K results from surface recombination of point defects which are generated on or below the surface by the irradiation and migrate to the surface at 110 K.