Copper has been neutron irradiated at temperatures in the range from 50degreesC to 250degreesC and subsequently stepwise annealed to about 600degreesC. The annealing behaviour was followed by Positron Annihilation Spectroscopy (PAS) and Transmission Electron Microscopy (TEM). In all cases an intense component with a positron lifetime of similar to 180 ps due to defects was observed by PAS as well as a high density of Stacking Fault Tetrahedra (SFTs) by TEM. The measured lifetime is longer than expected for perfect SFTs. Although the decrease in the positron trapping rate follows closely the decrease in SFT density, it is still not completely certain as to whether PAS detects mainly the SFTs and not some other vacancy-like defects.