Irradiation damage in nickel and iron in a high-voltage electron microscope and threshold energy determination

Iron and nickel thin foils have been irradiated in a high-voltage electron microscope. Interstitial dislocation loops are observed as a result of agglomeration of point defects produced by electrons. Comparison with theoretical results deduced from chemical reaction rate theory shows that nucleation is impurity controlled for nickel and that the binding energy of di-interstitials is low for iron. Measurements of the total cross section for producing free interstitials as a function of the incident electron energy have been performed. Comparison with calculated curves following the method developed by v. Jan and Seeger gives for threshold energies in the three directions the values T110 = 21 eV, T100 = 38 eV, T111 > 60 eV for nickel.