Positron annihilation spectroscopy evaluation of using proton irradiation as a surrogate for early neutron radiation damage

• Proton implantation can be used for a simulation of an early-stage neutron damage. • Temperature influences recombination and mobility of defects and hydrogen. • The ODS microstructure clearly affects on radiation stability and defect migration. • Hydrogen has a visible effect on the stabilization of vacancies. A positron annihilation spectroscopy investigation of early stages of radiation-induced damage in Chinese f/m (ferritic/martensitic) steel SIMP and strengthened variant of f/m steel ODS (oxide dispersion strengthened) EUROFER was conducted. Studied materials were irradiated by neutrons at the LVR-15 research reactor to 0.12 dpa at an average temperature of 260 ± 20 °C, and implanted by protons at the 6 MV Tandetron Accelerator of the Slovak University of Technology, to 0.0196 dpa at room temperature (RT) and 300 °C. The potential of using proton irradiation as a surrogate for early neutron radiation damage was investigated. A lifetime spectrometer and Doppler spectrometer was used to obtain simultaneously positron lifetime (PALS) and Doppler broadening spectra (DBS), which provided experimental data used to characterize the vacancy-type defect and their interaction with H atoms in the studied materials. The obtained results show an increase of mean positron lifetime (MLT) in the proton-implanted samples at RT when compared with high temperature irradiation. Similar trend was observed when comparing vacancy concentration of different irradiation conditions. The impact of temperature on mobility and recombination of defects, as well as effect of vacancy stabilization by H atoms, has been addressed. The effect of ODS microstructure on results has been examined. A methodology of comparing various irradiation conditions has been proposed, where the vacancy concentrations have been normalized by the dpa values. The potential application of proton implantation for evaluation of early stages of neutron damage was found to be promising.