[Show abstract][Hide abstract] ABSTRACT: Positron lifetime spectra were obtained from 1,1-bis(paramethoxy-meta- methyl- phenyl)-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.
Preview · Article · Jun 1999 · EPL (Europhysics Letters)
[Show abstract][Hide abstract] ABSTRACT: Positron lifetime measurements were carried out in normal hexane vs. temperature in the range of 12.5–62.5°C. The evaluation of the lifetime spectra indicates the presence of four lifetime components, as published first by Jacobsen et al. An attempt is made to interprete the properties of the longest-living two components in terms of the microscopic structure of the liquid.
No preview · Article · Mar 1995 · Journal of Radioanalytical and Nuclear Chemistry