Critical test of radiation-damage models by means of dislocation pinning experiments on copper

The hypotheses of one-dimensional migration and of thermal convertibility of the low-temperature interstitials in irradiated copper are critically tested by measuring the variation of internal friction and elastic modulus due to dislocation pinning as a function of the electron energy E in electron irradiation experiments (0.26 MeV ≤ E ≤ 0.7 MeV). The predictions of the crowdion model that one should observe a low threshold energy (ΔE 1 = threshold for production of on-line crowdions) at sufficiently high irradiation temperatures (T irr = 220 K), and a high threshold energy (Δ E 2 = threshold for production of off-line crowdions) at sufficiently low irradiation temperatures (Tirr = 75 K) or in annealing experiments following low-temperature irradiations, have been fully confirmed. Alternative interpretations in terms of the one-interstitial model are also discussed but are not very satisfactory. Furthermore, it is shown that, in addition to the two mentioned processes characterized by 10 eV ≤ Δ E 1 ≤ 14 eV and ΔE 2 = 17 eV, a third process with a lower threshold energy exists. This process appears to be temperature-independent between 75 and 220 K and is thought to correspond to the pinning of dislocations by defects produced either directly on or very close to the dislocations.