Positron annihilation acquired acceptance for structural investigation of solids but results in porous media-where positron lifetime spectroscopy (LT) reveals substantial Ps formation-were ambiguous. Data on zeolites lead to the conclusion that Ps trapping in competing "extended free volume" sites, inhomogeneous regions and grain boundaries occurs. Furthermore, positron trapping must also be considered. Systematic errors due to incomplete time range selection are discussed, significance and importance of corrections for 3γ/2γ counting efficiency differences are shown in practice.
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