Neutron Irradiated Copper: Is the Main Positron Lifetime Component due to Stacking Fault Tetrahedra?

Copper has been neutron irradiated at temperatures in the range from 50DGC to 250DGC and subsequently stepwise annealed to about 600DGC. 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 #~ 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.