Positron annihilation in thermally quenched potassium chloride

Positron annihilation lifetime and Doppler-broadened spectra have been obtained for thermally quenched KCl. It is found that internal consistency between the results of the two techniques is achieved when lifetime spectra are decomposed into four components. Using a simple statistical model for the annihilation of positrons it is deduced that the formation energy of Schottky defects is 2.1 \ifmmode\pm\else\textpm\fi{} 0.2 eV and further, that positrons trapped at vacancies have a lifetime of about 0.34 nsec. The two longest-lived components with lifetimes 0.77 \ifmmode\pm\else\textpm\fi{} 0.05 and 4.4 \ifmmode\pm\else\textpm\fi{} 0.02 nsec are shown to arise from annihilation of positronium. The positronium yield increases from about 16% at $T<150$\ifmmode^\circ\else\textdegree\fi{}K to about 25% at $T>250$\ifmmode^\circ\else\textdegree\fi{}K, the temperature region investigated being 90-296\ifmmode^\circ\else\textdegree\fi{}K. From Doppler-broadened spectra it is deduced that positronium is confined within a space of diameter 2 \AA{}.

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