Long-living positron and positronium states in zeolites and microcrystalline oxides

Abstract

Positron annihilation (PA) investigations were performed on zeolites (X, Y and ZSM-5) and on microcrystalline MgO, Al₂O₃ and SiO₂, providing long lifetime components attributed to o-Ps atoms. In addition to the positron lifetime (LT) measurement, the energy distribution (ED) of the annihilation gamma radiation spectrum was recorded in the 30 keV–1.5 MeV range for different samples and was compared to reference distributions for Si and GaAs samples, where no long-living Ps states are formed. Apart from the strong correlation with the water content in the samples, the positron data collected testify much more pronounced positronium hosting features for powders of the mentioned oxides than for zeolites. Positron LT spectroscopy combined with recording of the ED of the annihilation radiation provides reliable information on the formation of long living 3γ states.