3D Analysis of Helium‑3 Nanobubbles in Palladium Aged under Tritium by Electron Tomography

A 3D analysis at the nanoscale has been used to characterize helium-3 nanobubbles in palladium powders aged several years under tritium to assess their structural characteristics and spatial distribution. These helium-3 nanobubbles are formed by tritium radioactive decay and exhibit diameters centered around 2.5 nm. Scanning transmission electron microscopy (STEM) has been used to acquire tomographic series on typical zones of the macroscopic specimen containing helium nanobubbles. Electron tomography data treatments have been achieved, allowing 3D structural analysis of helium-3 nanobubbles. For the first time, interdistances between bubbles have been determined with a mean value between 8 and 10 nm. The swelling of the aged material varies between 8 and 18%, in agreement with macroscopic measurements and modeling.