Measurements of the electrical resistivity on almost dislocation free nickel specimens were performed during irradiation with 1.85 MeV electrons. Results obtained for irradiation temperatures varying between -80 and -40°C and for production rates varying between 2.10-11 and 5. 8 ∙ 10-10 dpas -1 are reported.
It was found that the electrical resistivity per Frenkel defect ρ, varies with the measuring temperature yielding a value of ρ = 2.33 ∙10 -4 Ωcm for TM = -60, 0°C.
Interstitials are not mobile for irradiation temperatures below Tirr = -60°C and quasi steady state defect concentrations are obtained in due time for irradiation temperatures higher than Tirr = -45°C. The results are compatible with the finding that the migration activation energy of interstitials decreases with increasing high energy particle flux i.e. from a value EIIM = 1.03 eV without irradiation to EIIM = 0.885 eV for a production rate of K = 3.46∙10 -10 dpas -1.
It was further found that di-interstitials are formed in situ when an existing interstitial encounters a dynamic crowdion. Di-interstitials are very mobile at an irradiation temperature of Tirr = -60°C initiating the formation of interstitial clusters which are enriched in undersized impurity atoms, e.g. in silicon.
In the presence of large interstitial clusters or precipitates the migration activation energy of interstitials decreases further e.g. a value of EIIM ≤ 0.82 eV is found for specimens irradiated for τirr = 2∙106 s.