Defects in electron irradiated Ct-Si were studied by the positron anni
hilation technique. In order to know effects of the thermal history of
crystals on the introduction of defects, the specimen was quenched fr
om 1390 degrees C to room temperature before irradiation. A clear corr
elation between results obtained by the positron annihilation experime
nts and those by infrared spectroscopy was established. From the isoch
ronal annealing experiment, it was found that oxygen clusters were int
roduced by quenching treatments.