On recoil energy dependent void swelling in pure copper

In recent years, the problem of void swelling has been treated within the framework of the production bias model (PBM). The model considers the intracascade clustering of vacancies and self-interstitial atoms (SIAs), their thermal stability and the resulting asymmetry in the production of free and mobile vacancies and SIAs. The model also considers the influence of one-dimensional diffusional transport of glissile clusters of SIAs on damage accumulation in the form of voids and defect clusters. One of the major predictions of the PBM is that, at a given irradiation temperature and damage rate, the void swelling should depend sensitively on the recoil energy, since it affects strongly the intracascade clustering of SIAs and vacancies, particularly at lower recoil energies. In order to test the validity of this prediction directly by experiment, pure and annealed copper specimens were irradiated with 2.5 MeV electrons, 3 MeV protons and fission neutrons at about 520 K. All three sets of irradiation experiments were carried out with a similar damage rate (of the order of 10(-8) NRT dpa s(-1)). Post-irradiation defect microstructures were investigated using electrical resistivity, transmission electron microscopy and positron annihilation spectroscopy. The accumulation of defects in the form of planar clusters and voids is found to increase substantially with increasing recoil energy. This is in good accord with the predictions of the PBM.