Positronium formation in low-density polyethylene (LDPE)

Positron annihilation lifetime spectroscopy has been applied to low-density polyethylene (LDPE) as a function of the temperature and also the elapsed time in the dark as well as in the light. Positronium formation below, around and above the glass transition temperature of LDPE was investigated. It was found that far below the glass transition temperature, T-g, the o-Ps intensity increased with the elapsed time in the dark. It was interesting to observe an initial rapid increase in the o-Ps intensity, followed by a continuous decrease with the elapsed time, especially at around T-g. Above T-g, the o-Ps intensity decreased very slowly with the elapsed time at 250 K and almost did not decrease at room temperature. Furthermore, no increase, but only a decrease, in the o-Ps intensity with the elapsed time was seen in light. Possible explanations of these effects were discussed. A simple calculation of the activation energy of the trapped electrons was suggested. (C) 2003 Elsevier Science B.V. All rights reserved.