Positron lifetime measurements of the vacancy properties of annealed and electron-irradiated aluminium

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Abstract
BaF2 detectors have been utilised to obtain extremely precise lifetime data for annealed Al in the range of 293-903 K, and for Al, electron-irradiated at T<117 K, as a function of isochronal annealing. The vacancy formation and migration energies are generally consistent with those of previous studies, although both simple trapping model analyses and an examination of the data in terms of pre-thermal trapping suggest that the specific trapping rate increases above 600 K. From observations of the high temperature measurements it is concluded that positron trapping at equilibrium divacancies is, at most, of only minor significance. The results from both the annealed and irradiated samples show that the vacancy trapped lifetime is essentially independent of temperature for large vacancy concentrations. However, at low equilibrium vacancy concentrations there is a tendency for the trapped positron lifetime to rise above its 'normal' value.