MeV proton irradiation damage in Ta: Measurements, characterization and comparison to W

Abstract The effects of high-energy proton irradiation on tantalum and its properties, were studied at the Soreq Applied Research Accelerator Facility (SARAF) using a high-flux 2.2 MeV proton beam. Samples were characterized by optical interferometry, nano-indentation and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS), to study the effect of radiation damage. The experimental data on the penetration depth of 2.2 MeV protons in tantalum was found to be in good agreement with simulations and an increase of the irradiated sample’s hardness was measured. The volume expansion was found to be correlated to the total proton fluence. With the aid of density functional theory estimates of the point defect formation volumes, we suggest that hydrogen occupies mainly interstitial sites in the Ta lattice. We observed extensive diffusion of the hydrogen into the material. Thus, no blistering was observed up to a total fluence of 1.9•1020 P/cm2, extending the lower bound for blister formation in tantalum to one to three orders of magnitude above the critical fluence for blistering in tungsten. A reaction-diffusion model was employed to analyze the spatial distribution of the point defects, to assist in the interpretation of the results in comparison with tungsten, and to identify the role of the hydrogen diffusion. We conclude that tantalum is a promising structural material in proton radiation environments.