Exchange of injected hydrogen isotopes between diffusing and trapped states in Al

Abstract
Exchange of hydrogen isotopes between diffusing and trapped populations was found with successive injections of 25 keV D2 + and 100 or 140 keV H2 + into Al surface by simultaneously detecting elastically recoilled hydrogen and deuterium using 2 MeV He+. When backward diffusion of injected hydrogen toward surface was supposed to be impeded or by-passed by structural changes in the subsurface layer due to ion bombardment, effective replacement cross-section of about 1.4 × 10−18 cm2 was observed. Otherwise, namely when the hydrogen backward diffusion is supposed to be rather free, the effective cross section of about 7.8 × 10−18 was observed. Due to the difference in energy of the first and second injections, this phenomenon is different from that so called “isotopic exchange”, which occurs through collisional process.