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Competitive positron and positronium trapping in porous media
Kajcsos, Zs.; Liszkay, L.; Duplâtre, G.; Lázár, K.; Lohonyai, L.; Varga, L.; Gordo, P. M.; Lima, A. P. de; Gil, C. Lopes de; Marques, M. F. FerreiraPositron annihilation acquired acceptance for structural investigation of solids but results in porous media--where positron lifetime spectroscopy (LT) reveals substantial Ps formation--were ambiguous. Data on zeolites lead to the conclusion that Ps trapping in competing "extended free volume" sites, inhomogeneous regions and grain boundaries occurs. Furthermore, positron trapping must also be considered. Syste...
Positron and positronium in porous media: zeolites
Kajcsos, Zs.; Liszkay, L.; Duplâtre, G.; Lohonyai, L.; Varga, L.; Lázár, K.; Pál-Borbély, G.; Beyer, H. K.; Caullet, P.; Patarin, J.; Lima, A. P. deCorrelations 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....
Effect of water-soluble electron scavengers on positronium formation in AOT/wat...
Subrahmanyam, V. S.; Marques, M. F. Ferreira; Duplâtre, G.In a previous work reporting on positron annihilation lifetime spectroscopy (LS) measurements in AOT/water/isooctane microemulsions, a model was established leading to the satisfactory description of both triplet positronium (o-Ps) formation and decay. The model proposes that a large proportion of Ps is formed in the aqueous pseudophase, a fraction of which can diffuse out to the organic phase. It thus predicts...
Size of Sodium Dodecyl Sulfate Micelles in Aqueous Solutions as Studied by Posi...
Duplâtre, G.; Marques, M. F. Ferreira; Miguel, M. da GraçaThe micelles formed by sodium dodecyl sulfate (SDS) are studied in aqueous solutions at 294 K as a function of nominal SDS concentration (C) using positron lifetime spectroscopy. In a four-component analysis of the data, it appears that the lifetime (τ3) of the positronium triplet state (o-Ps) in the aqueous phase decreases significantly with increasing C. Preliminary results on sodium methanesulfonate solution...
Four-Component Analysis and Modeling of Positron Annihilation Lifetime Paramete...
Marques, M. F. Ferreira; Burrows, H. D.; Miguel, M. da Graça; Lima, A. P. de; Gil, C. Lopes; Duplâtre, G.Reverse micelles are studied in sodium AOT/water/isooctane mixtures as functions of AOT concentration (CAOT), water to AOT mole ratio (w0) and temperature (T), from 294 to 333 K, using positron annihilation lifetime spectroscopy (LS). By four-component analysis of the spectra, it is possible to extract the LS parameters (intensities, Ii, and lifetimes, τi) of the triplet positronium (o-Ps) present in the aqueou...
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