Vacancy-type defect production in iron under ion beam irradiation investigated with positron beam Doppler broadening technique

Accumulation of vacancy-type defects in iron produced by various ion irradiations at room temperature was investigated with positron beam Doppler broadening technique. Various ion species (He, C, O, Fe) were used for investigation of the effect of PKA energy on vacancy-type defect production. Accumulation of vacancy-type defects leads to sharpening of Doppler broadening spectra, i.e., increase of S parameter. S parameter was measured as a function of ion fluence for various ion species at a fixed positron energy of 15 keV. At the early stage of irradiation, S parameter increases with increasing fluence, and then it reaches some saturated S parameter value that varies with ion species. The saturated S parameter values tend to be higher for heavier ion irradiation. When compared with the incremental change of S parameter at the same low dpa level, heavier ions also lead to a greater change.