Positron annihilation in pure and defected metals

Abstract

The Doppler-broadening technique has been applied to positron annihilation studies in plastically deformed and annealed specimens of zinc, indium, cadmium, lead, gold, and silver in the temperature range down to 4.2 K.

Annealing studies in metals deformed at room temperature or under liquid nitrogen provided information on recrystallisation and on the nature of defects produced by plastic deformation. It has been shown that the specific trapping rate of positrons by deformation-induced dislocations is temperature independent.

The equilibrium measurements, which extended up to their melting points in well annealed samples (except for gold and silver) , enabled us to compare the models proposed to take into account the intermediate temperature dependence of the line-shape parameter. Also the mono-vacancy formation energies could be determined.

The model fittings to the annihilation gamma-ray peak, which consisted of a Gaussian and an inverted parabola convoluted with the instrumental resolution function, provided the probabilities of positron annihilation with core and conduction electrons in the deformed and annealed samples.

The annihilation spectra were recorded with a high resolution Ge(Li) detector whose resolution at a count rate of 5000 cps was 1.15 keV for the 514 keV line in 85Sr.

Further results on the temperature dependence of the width parameters of the Gaussian and parabolic distributions which characterise the momentum distributions of the core and conduction electrons, respectively, are presented.