Measurements of the value t2 and the intensity I , of the long component in the lifetime spectra of positrons annihilating in some simple unassociated, polar, and associated organic liquids are reported as a function of temperature. A semi-empirical free volume model for the formation and quenching of ortho-positronium atoms is developed for simple molecular materials to explain the correlation between viscosity 7, density e, and re observed in unassociated and polar liquids. Such a correlation is not observed for associated liquids in which the presence of hydrogen bonds between molecules apparently influences the annihilation process. The data of positron lifetimes during the solid-liquid phase transition in some organic systems are discussed in terms of the free volume model. Es werden Messungen des

No abstract

No abstract

No abstract

Positron lifetime spectra in teflon are measured as a function of γ‐dose from 3000 Ci cobalt‐60 assembly. The irradiations and positron lifetime measurements are carried out, both in air and vacuum. The values of lifetimes τ1, τ2, τ3 and their respective intensities I1, I2, and I3 are determined with the help of three component fit. Electron spin resonance, density, dielectric constant, and nuclear magnetic resonance measurements are also carried out on teflon samples irradiated in a similar way. Initial γ‐dose results in increased free volume of voids, where orthopositronium rests. Hence the lifetime τ3 increases. As the dose is increased further quenching effect of free radicals becomes dominant and lifetime of positronium decreases. Similar trend is observed in dielectric constant and NMR data.