Temperature dependence of the positron annihilation in liquid and solid bismuth and gallium

Abstract

The annihilation rate is measured for liquid and solid Bi and Ga at the peak of angular correlation curve. Linear increase of this rate observed up to the melting point confirms the lack of positron trapping in solid Bi and Ga. At the melting point a nearly 20% increase of the counting rate is observed for Ga, while for Bi about 5% decrease is noticed. The anomalies found in the F(T) curve for the liquid phase are associated with the existence of cluster atoms and with the process of their structure rebuilding. With the exception of small momenta ranges there are no noticeable variations of the electron momentum distribution measured at different temperatures.