Small-angle X-ray scattering measurements of helium-bubble formation in borosilicate glass

Small-angle X-ray scattering (SAXS) measurements have been performed to study helium-bubble formation in borosilicate glass. Helium was introduced by He⁺ implantation over an energy range of 1 to 2 MeV to give a uniform distribution over ∼1 µm depth. The implanted dose was varied from 9 × 10¹³ to 2.8 × 10¹⁶ ions cm⁻², corresponding to a local concentration range of 40 to 11200 atomic parts per million (a.p.p.m.) averaged over the implantation depth. The SAXS response was fit with the Percus–Yevick hard-sphere interaction potential to account for interparticle interference. The fits yield helium-bubble radii and helium-bubble volume fractions that vary from 5 to 15 Å and from 10⁻³ to 10⁻¹, respectively, as the dose increased from 9 × 10¹³ to 2.8 × 10¹⁶ cm⁻². The SAXS data are also consistent with maximum helium solubility with respect to bubble formation between 40 and 200 a.p.p.m. in the borosilicate glass matrix.