Positron and positronium annihilation patterns in zeolites and bulk ceramics

Abstract

Positron lifetime (LT) measurements have revealed that in porous media the annihilation pattern is probably dominated by a near-saturation level trapping both for the positron and the positronium as well, which masks the contribution from the ldquofree annihilationrdquo, i.e., annihilation from delocalised positrons. In this work we compare positron lifetime spectra of crystalline zeolites with bulk ceramic materials fabricated by sintering from the same constituents as the zeolites and analyse common features and differences between them. For the dense ceramic samples the contribution from long-living components to the annihilation pattern is substantially lower than that for the zeolites. The results are analysed with the aim to extract new knowledge for the zeolites and for the sensitivity limits for free volume studies in ceramics. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)