Positronium formation in NaY-zeolites studied by lifetime, positron beam Doppler broadening and 3-gamma detection techniques

Abstract

Results of positron annihilation measurements on NaY pressed powders and deposited thin films using slow positron beam and conventional fast positron techniques are presented. In lifetime experiments using an external 22Na source an averaged long lifetime of 1.8 ns with a sum intensity of 27% was observed in pressed powders in the presence of air at room temperature (RT). In literature this lifetime is ascribed to positrons annihilating in water filled α or β cages Habrowska, A.M., Popiel, E.S., 1987. Positron annihilation in zeolite 13X. J. Appl. Phys. 62, 2419. By means of isotopic exchange some of the Na was replaced by 22Na. These powders showed a long lifetime component of 7–8 ns with an intensity increasing from 1 to 12% when heated under normal atmosphere from RT to 200°C. No significant increase of the shorter (1.5 ns) lifetime was observed, while its intensity dropped from 13.4 to 6.6%. Both effects are ascribed to the loss of water from α cages only. The beam experiments revealed a high fraction of 3-gamma annihilations in the pressed powder and thin film samples, indicating the annihilation of o-Ps and thereby the existence of large open volumes.