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  • 1 ITA Institut für Innovative Technologien Köthen Außenstelle Halle, Edvard-Grieg-Weg 8 D-06124 Halle/S (Germany)
  • 2 Helsinki University of Technology Laboratory of Physics SF-02150 Espoo (Finland)
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Abstract  

Positron lifetime (LT) and Doppler-broadening (DB) studies of polyethylene have been performed simultaneously in the temperature range between 80 and 300 K. The LT spectra have been analysed assuming four exponential components. Two long-lived components appear, which were attributed too-Ps pick-off annihilation in crystalline regions (

\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\tau _{\Delta _3 } = 1.5$$ \end{document}
to 2.8), The variation in 4 correponds to an increase of the mean hole size from 0.053 nm3 at 80 K to 0.188 nm3 at 300 K. From the data the glass transition temperature (Tg=195 K), the coefficient of thermal expansion of holes in the glassy and rubbery phase (h, g = 14.5 · 10–4 K–1 and h, r = 189 · 10–4 K–1) and the fractional free volume (2.8% to 10.4%) were estimated. The DB curves were fitted by a sum of three Gaussians, the narrowest of which is assumed to represent the self-annihilation ofp-Ps localised at holes. The intensity of the narrow component,In, varies between 0 and 7.3% in a similar way as the LT intensityI4/3 varies. From this it was concluded that other Ps reactions beside pick-off are not important. Further, it was shown that the average positron lifetime is dominated by theo-Ps component,T4g, while the behaviour of the DB peak height is mainly affected by thep-Ps narrow componentIn.