A model for interpreting the positron annihilation characteristics of deformed metals; application to vanadium

Abstract

The positron characteristics in the temperature range 10-300 K have been investigated for single crystals of vanadium deformed under different conditions. Positive temperature dependences for the annihilation parameters S and are found. The average rate of increase appears to be controlled by the dislocation density and concentration of vacancies induced by deformation. A positron trapping model, assuming trapping at dislocations decreasing exponentially with temperature, thermally activated detrapping from dislocations and temperature-independent trapping at deep traps, predicts a temperature-dependent competing trapping that determines the temperature dependences of the annihilation parameters. The validity and predictions of the model are discussed in terms of the parameters of the functions S(T) or . The positron binding energy for dislocation lines, their positron trapping coefficient, the dislocation density and the rate of trapping at deep traps can be determined by fitting the observed temperature dependences to this competing-trapping model. The method permits us to investigate quantitatively the evolution of the defect structure of metals during their recovery.