Positron Annihilation in Solid and Molten Alkali Chlorides

Abstract

The time annihilation spectra of positrons were measured in solid and liquid NaCl, KCl, and CsCl at temperatures between 295 and 1223°K. An abrupt change of the spectral shapes is observed at melting. It was possible to show that the so-called $A$-center model, which is based on the assumption that the positron can be captured by a lattice defect, can account for this effect. In the framework of the $A$-center model, an effective electron number has been calculated which increases when passing from LiCl to CsCl.