He Bubble Concentration, Size and Strain in Implanted Aluminum by SAXS/WAXS

Alpha-radiation damage in metals is a concern for long-term radioactive storage and systems that produce nuclear energy. Accurate prediction of irradiated material properties and failure mechanisms depends on a fundamental understanding of the size and relative percentage of helium (He) bubbles. X-ray scattering experiments are a valuable tool to resolve the nanobubble morphology (of ~ 10(11) bubbles) and crystallographic strain as a function of He implantation energy and concentration in aluminum (Al) foils. A proportional change in bubble volume fraction is observed with He concentration within the same sample, while only a slight increase in the mean bubble size is observed. Estimates of the He fraction in the bubble phase with sizes ~ 4 nm, along with the overall crystallographic strain, suggest a proportion of the total implanted He exists as small bubbles (~ 1 nm) and possibly as defects in the crystal lattice. However, the fraction of He in 4-nm nanobubbles increases significantly when the He energy is above the Coulomb barrier of Al.