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Activation energy for long-range migration of self-interstitial atoms in tungsten obtained by direct measurement of radiation-induced point-defect clusters

The activation energy for the long-range intrinsic migration of self-interstitial atoms (SIAs) in metals, , is an important physical quantity closely associated with microstructural evolution upon energetic particle irradiation. The values for various metals have been widely investigated through recovery experiments on specimens irradiated at low temperatures upon thermal annealing, and the values have been estimated from the dependence of measured quantities of the specimens on the annealing temperature. On the other hand, the dependence of measured quantities on irradiation temperature is also expected to reflect the values. It is of importance to compare the values obtained by these two different kinds of experiments. However, no systematic studies have been carried out along the latter line. In this study, the number densities of SIA clusters formed in tungsten upon high-energy electron irradiation are directly measured as a function of the irradiation temperature using high-voltage electron microscopy. The analysis of the experimental data shows that the value is in the range from 0.088 to 0.102 eV or it is less than 0.046 eV. These values are consistent with those obtained in a recovery experiment and a theoretical study, respectively.