Positron lifetime spectra were obtained from 1,1-bis(paramethoxy-meta- methylphenyl)-cyclohexane (BMMPC) vs. temperature T between 23 and 348 K. At low temperatures, almost up to the glass transition at Tg, a fast pick-off annihilation mechanism is proposed for explaining the variations in the annihilation parameters of positronium (Ps). Above the Vogel temperature T0 the lifetime of o-Ps is coherently interpreted in terms of a thermodynamic model which assumes the molecules to occupy solid- and liquid-like states. The transition temperature of the model calculated from o-Ps lifetimes is significantly less by ∼ 20 - 30 K than that obtained from all other physical quantities available, including free positron lifetimes.
ASJC Scopus subject areas
- Physics and Astronomy(all)