Helium bubble in aluminium studied by positron annihilation: determination of bubble parameters

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Abstract
The paper demonstrates that it is possible to obtain information from the positron annihilation technique about rare-gas bubbles in metals, i.e. the gas density inside bubbles and the average bubble size and concentration. This is done by a detailed study of aluminium in which He bubbles are introduced by irradiation at temperatures in the range 375-485 K with 600 MeV protons. The samples are studied both in the as-irradiated state and after annealing at temperatures up to 873 K. Evaluation of bubble parameters is made from positron lifetime results employing a theoretical relation between positron lifetime and He density in bubbles and a semi-empirical relation between positron-specific trapping rate and cavity radius. Results are compared with determinations of bubble parameters by other experimental methods. In addition, one-dimensional angular correlation curves for He bubbles as a function of He density are determined.