We have measured microscopic 3-dimensional distribution of plasma-charged hydrogen in polycrystalline Al. The measurements have been carried out nondestructively by using elastic recoil detection analysis under transmission geometry of a collimated 8 MeV 4He2+ beam. The recoil cross section as large as 2 × 103 mb/sr due to the nuclear elastic collision allowed observation of the spatial distribution of hydrogen in the Al sample of 80 μm thickness. The distribution maps of hydrogen clearly visualize hydrogen bubbles of 10–20 μm diameter in the surface layer of about 12 μm thickness. The critical concentration of hydrogen minimally needed for growth of the hydrogen bubble of ten-μm size has been determined to be 1.6 × 1020 cm−3.
