Positron annihilation lifetime and Doppler broadening correlations for a variety of polymers, cross linked rubbers and organic liquids

We have used positron annihilation Doppler broadening spectroscopy and positron annihilation lifetime spectroscopy to investigate properties of several polymers, vulcanized rubbers and organic liquids. The Doppler broadening is characterized by the S parameter, which is a measure of the probability of low momentum annihilations in the material. The lifetime spectroscopy is characterized by the ortho-positronium (o-Ps) pickoff lifetime and intensity of o-Ps formation. There is an interesting correlation between the S parameter and the probability of o-Ps formation that is dependent on polymer composition and sensitive to oxygen or fluorine present in the polymer. A similar conclusion has also been recently reported by another group. We also point out several correlations between the positron response and various physical parameters characterizing the materials. The cross linked rubbers behave differently from the polymers and more like liquids, exhibiting an essentially constant S parameter. (c) 2007 Elsevier B.V.. All rights reserved.