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

Results of positron annihilation measurements on NaY pressed powders and de posited thin films using slow positron beam and conventional fast positron techniques are presented. In lifetime experiments using an external Na-22 s ource an averaged long lifetime of 1.8 ns with a sum intensity of 27% was o bserved in pressed powders in the presence of air at room temperature (RT). In literature this lifetime is ascribed to positrons annihilating in water filled alpha or beta cages Habrowska, A.M., Popiel, E.S., 1987. Positron a nnihilation in zeolite 13X. J. Appl. Phys. 62, 2419. By means of isotopic e xchange some of the Na was replaced by Na-22. These powders showed a long l ifetime component of 7-8 ns with an intensity increasing from 1 to 12% when heated under normal atmosphere from RT to 200 degrees C. No significant in crease of the shorter (1.5 ns) lifetime was observed, while its intensity d ropped from 13.4 to 6.6%. Both effects are ascribed to the loss of water fr om alpha cages only. The beam experiments revealed a high fraction of 3-gam ma annihilations in the pressed powder and thin film samples, indicating th e annihilation of o-Ps and thereby the existence of large open volumes. (C) 2000 Elsevier Science Ltd. All rights reserved.