Positron lifetimes and trapping probabilities observed separately for vacancies and dislocations in aluminium

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Abstract
The annihilation characteristics of positrons in aluminium have been studied for the distinct cases of annihilation in the perfect lattice and annihilation after trapping at vacancies or dislocations. A controlled production of vacancies and dislocation in single crystal aluminium specimens was achieved with a quenching and annealing procedure. The annihilation lifetime in the perfect lattice is 166+or-2 ps, whereas it is 246+or-4 ps for positrons trapped in vacancies and 250+or-30 ps for positrons trapped in dislocations. The mean lifetime is found to increase with increasing dislocation density, but saturation is not attained with the dislocation densities obtainable by the quenching process. The trapping probabilities are (0.23+or-0.05)*1015 s-1 for vacancies and (0.08+or-0.05)*1015 s-1 for dislocations.