Positron and positronium in porous media: zeolites

Abstract

Correlations between positronium (Ps) production features and positron annihilation (PA) parameters were investigated in various zeolite samples (MFI, mordenite, Na-Y). The contribution of 3[gamma]-annihilation on data registration was closely examined. Long lifetimes up to 135 ns and triplet Ps (o-Ps) fractions up to 30% were found. Even low amounts of adsorbed gases or water drastically change the PA pattern. It is concluded that in addition to the crystallographic free sites, large structural discontinuities also play an important role as they can trap Ps and provide it with vacuum-like survival conditions.