On recoil energy dependent void swelling in pure copper - Part I. Experimental results

In recent years, the problem of void swelling has been treated within the f ramework of the production bias model (PBM). The model considers the intrac ascade clustering of vacancies and self-interstitial atoms (SIAs), their th ermal stability and the resulting asymmetry in the production of free and m obile vacancies and SIAs. The model also considers the influence of one-dim ensional diffusional transport of glissile clusters of SIAs on damage accum ulation in the form of voids and defect clusters. One of the major predicti ons 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, partic ularly at lower recoil energies. In order to test the validity of this pred iction directly by experiment, pure and annealed copper specimens were irra diated 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 si milar damage rate (of the order of 10(-8) NRT dpa s(-1)). Post-irradiation defect microstructures were investigated using electrical resistivity, tran smission electron microscopy and positron annihilation spectroscopy. The ac cumulation of defects in the form of planar clusters and voids is found to increase substantially with increasing recoil energy. This is in good accor d with the predictions of the PBM.