Positron Annihilation in Potassium Chloride and Potassium Iodide

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Abstract
Positron lifetime spectra have been measured in several single crystals of KCI and KI. Angular correlation measurements of 2 γ annihilation radiation have been made in polycrystalline materials. The positron wave function calculated by the spherical symmetric Wigner‐Seitz approximation in the neighbourhood of the anion is similar to that in metals and indicates that positrons are free in alkali halides. The experimental angular correlation curves are much narrower than those calculated with positrons in crystalline states, when Wigner‐Seitz wave functions of the positron were used and only annihilations with anion shells were taken into account. The assumption that positrons are trapped by crystal defects explains the observed differences in lifetime measurements. The angular correlation curve caused by trapped positrons has been constructed by subtracting the calculated momentum distribution of the ground state positrons in the crystal bulk from the total experimental curve.