DEUTERIUM DIFFUSION, TRAPPING AND RELEASE IN ION-IMPLANTED BERYLLIUM

High purity beryllium samples were loaded with deuterium by ion-implantation at 25-degrees-C or by thermal absorption in D2 gas at 300-500-degrees-C. The samples were then thermally ramped up to 800-degrees-C at rates of 2-3-degrees-C/min, and the released deuterium measured as a function of temperature using a mass spectrometer. An alternative technique used was He-3-D nuclear reaction analysis, which measures the amount of deuterium retained in the near-surface (0-1-mu-m). Some samples were pre-implanted with 10(15) mm-2 30 keV He+ ions to create extra trapping centres. The data have been compared to various diffusion model calculations in an attempt to extract trapping energies and concentrations. From the analysis it has been determined that the effects of surface oxide must be included in the calculations. Rutherford backscattering analysis was used to measure the oxide thickness at each stage of the experiment: generally the oxide layer was 2-10 nm thick before loading the deuterium, 10-20 nm thick after loading, and 15-30 nm thick after desorbing the deuterium. The oxide growth was attributed to residual water vapour in the vacuum systems.