Free volume effects are important for positronium formation, pick-off annihilation and chemical reactions. The relation between the long-lived component intensity and the number of defects is considered for the case of selective localization of positrons and positronium in ordered and disordered sites of plymers. Positronium lifetimes for the large pores (r
1 nm) are discussed. In positronium chemical reactions recent results show crucial role of the bubble parameters in liquids.
A bound state of positron (e+) and electron (e-) (positronium Ps) can be considered as a kind of hydrogen-like atom and the simplest free radical, which has a positron instead of a heavy nucleus. Annihilation g-radiation is in fact a label of this short-lived atom. Therefore, positronium chemistry is radiochemistry of the lightest short-lived labeled atom. Application of positronium chemistry to various chemical problems is essentially dependent on our knowledge of analogies and differences in the formation and chemical conversion of Ps, a atomic hydrogen, and other free radicals. In this review, experimental results of the authors and some other publications are briefly analyzed from this point of view.
Authors:Ch. He, E. Hamada, T. Suzuki, H. Kobayashi, K. Kondo, V. Shantarovich, and Y. Ito
A new pulsed mono-energetic slow positron beam as well as the conventional positron annihilation lifetime spectroscopy (PALS) have been applied to study the sub-surface and the bulk of epoxy polymer. Significant changes of o-Ps parameters were found at a short distance from the surface. The lifetime of o-Ps was observed to decrease with increasing the positron implantation depth, while its intensity increased. The temperature effect on o-Ps parameters at sub-surface was also investigated. The glass transition temperature for the sub-surface was lower than that for the bulk. Furthermore, the thermal expansion coefficient of the sub-surface was found smaller than that of the bulk.
Authors:V. Shantarovich, T. Suzuki, Y. Ito, K. Kondo, V. Gustov, A. Pastukhov, L. Sokolova, A. Polyakova, E. Belousova, and Yu. Yampolskii
Elastic and glassy polymers are normally considered as homogeneous disordered materials with unimodal (statistical) distribution
of elementary free volumes. In this work, we discuss the results of our positron annihilation lifetime (PAL) measurements
for a number of elastic and glassy polymers, where observations of the two long-lived ortho-positronium components in the
PAL spectra and irregular (nonlinear) variations of annihilation characteristics in the vicinity of glass transition temperature
reveal structural heterogeneity of these systems. The conclusion is confirmed by measurements of thermo-stimulated luminescence,
thermo-mechanics and mobility of penetrants.