Defect formation in iron by MeV ion beam investigated with a positron beam and electrical resistivity measurement

This study involves the investigation of defect production in iron involving cascade damage processes produced by MeV ion irradiation. Defect configuration after cascade damage is expected to be preserved at low temperatures below Stage I where interstitial atoms begin to migrate. MeV ion beam irradiation of pure iron was carried out at 12 K, and then positron beam Doppler-broadening measurements and electrical resistivity measurements were carried out at the same temperature. By these methods, defect production efficiency, which is defined as the ratio of residual defects to defect formation calculated by the Norgett-Robinson-Torrens (NRT) model, was evaluated for iron irradiated with protons and carbon ions. The defect production efficiency values from the electrical resistivity and the computational calculation coincide well to support the validity of the computational approaches to the phenomenon. The values from the positron beam qualitatively represent the difference in the primary knock-on atom (PKA) energy spectrum of H+ and C+, but the values were lower than those obtained from the electrical resistivity measurements and the computational calculation, possibly due to inhomogeneous distribution of vacancies caused by cascades and enhanced mutual annihilation of Frenkel pairs.