Interpretation of positron-annihilation experiments on electron-irradiated α-iron in terms of self-interstitial migration in stage III

A recent interpretation of positron annihilation in electron-irradiated α-iron in terms of free migration of monovacancies in Stage III is shown to be internally inconsistent and incompatible with well-established experimental results, in particular with the monovacancy migration enthalpy deduced from high-temperature equilibrium data. The positron-annihilation experiments find a natural explanation in terms of self-interstitial migration in Stage III. This interpretation accounts not only for the gross features but also for fine details of the positron-annihilation data. It is shown to be in excellent agreement with the results of internal-friction studies on irradiated a-iron. The present analysis supports strongly the previous suggestion that in α-iron two self-interstitial configurations exist, one migrating freely in Stage IE and the other one in Stage III. A further conclusion is that positrons in α-iron can be trapped not only by vacancy-type defects and dislocations but also by clusters of self-interstitials or/and of carbon atoms.