The free positron lifetime in amorphous polymers at low temperature

Abstract

A series of amorphous polymers was studied by positron annihilation lifetime (PALS) spectroscopy at 20K each experiment lasted more than 1week. The lifetime spectra were deconvoluted into three exponential components. In isothermal conditions, an increase of the free positron lifetime is observed while the parapositronium (pPs) and orthopositronium (oPs) lifetimes do not change with the measuring time. This upward trend was correlated to the oPs intensity change. To explain the time dependence of the free positron lifetime, a model based on heterogeneities in the electronic density and accumulation of shallowly trapped electrons (STEs) caused by the 22Na source irradiation is proposed. The fittings give two parameters the intrinsic free positron lifetime τ 20 and the Onsager radius R0PALS. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.