Positronium trapping in free volume of polymers

Positronium trapping process caused by slow thermalization of Ps inside int ermolecular spaces of polymer is considered. The pickoff annihilation rate of Ps decreases from an initial value, characteristic for the delocalized P s, to a final value, relating to its localized state. The elastic thermaliz ation lifetime analysis of polymers spectra with a new ETLT program is prop osed to determine the total Ps intensity (IPs), Ps trapping rate (gamma), i ts initial (tau(0)) and final (tau(infinity)) pickoff lifetimes as well as the relative e(+)-e(-) contact density (eta) The model is tested through th e analysis of polyurethane spectra measured in a wide range of temperature, containing the glass transition point (T-g). In contrast to the convention al analysis, I-Ps does not display any change at T-g. The results indicated slow trapping rate (about 1 ns(-1)) of Ps in the cavities. (C) 2000 Elsevi er Science Ltd. All rights reserved.