Effect of Fe content on positron annihilation in neutron irradiated V-Fe alloys

Neutron irradiated V-xFe alloys (with x from 0 to 5 at.%) have been studied by the conventional positron annihilation technique. A remarkable narrowing of angular correlation of annihilation radiation (ACAR) curves was observed for all alloys investigated. A specific feature of ACAR curves in pure vanadium is the presence of a narrow component attributed usually to the positronium (Ps) formation in voids, with inner surfaces covered by gaseous impurities such as oxygen. Significant changes in the ACAR curve component intensities with increase of iron content has been observed. At Fe concentration of about 1 at.% the narrow component disappears completely and the intensity of the middle one decreases significantly. It was concluded that the increase of Fe concentration in V-Fe alloys suppresses the void surface contamination by oxygen atoms and changes the positron work function from bulk materials into voids. Such behavior of the ACAR curve component intensities can be explained in terms of radiation-induced segregation of iron atoms at point defect sinks. (orig.)