Small defects observed by IR light-scattering tomography after short-time annealing were shown to be related to the nuclei of ring-distributed oxidation-induced stacking faults (ring-OSF) in Czochralski-silicon crystals grown with growth rates of about 0.8 mm/min. The behavior of these defects was studied under different annealing conditions, and it was found that they were already present in the as-grown crystal below the detection limit of available techniques. Preannealing in nitrogen at 1150 degrees C introduced a stacking-fault-free region with subsequent oxidation. The reason for this was due neither to the annihilation of the ring-OSF nuclei nor to the formation of punched out dislocation loops from precipitates during nitrogen ambient annealing, but probably due to a change in the nature of the OSF nuclei occurring, making them incapable of OSF nucleation during subsequent oxidation. Various small defects were observed to exist in the as-grown crystal, and the radial position of these defects depended on their critical size. The distribution of as-grown defects within the crystal reflects the differences in the thermal stability of the defect nuclei due to point defect variations in the crystal during growth.