Positron annihilation in liquids and in solutions containing electron acceptors and charge-transfer complexes

Positron lifetime measurements and angular correlation measurements were performed in several organic liquids. The results strongly indicate that positronium is contained in a "bubble" in the liquids. The radius of the bubble can be estimated by using the broadness of the narrow component in the angular correlation distribution, and by using the surface tension of the liquids. Both methods give bubble radii from 4-7 Å in the solvents investigated. The bubble influences the reaction mechanism between Ps and weak electron acceptors in such a way that the presence of the bubble decreases the reactivity of Ps. Positron lifetime measurements were also performed on a series of mixtures of organic liquids and on electron acceptors and charge-transfer complexes in solution. The results were in agreement with the spur reaction model of Ps formation, which, for the binary mixtures, explains the influence on Ps formation of proton spur reactions, in other cases of the solvation of spur electrons and positrons, and finally of electron trapping on CS combined with high electron mobility in pure CS. The electron trapping ability of CS is expected to depend on the V of the solvent in which the CS is dissolved. This dependence was observed. The electron acceptors give rise both to Ps inhibition (with two possible exceptions) and quenching, but when an acceptor takes part in m charge-transfer complex, the inhibition intensifies and the quenching almost vanishes. The decreased quenching was used to determind complexity constants that were in reasonable agreement with constants obtained from optical data. PV technique was also introduced to determine gas phase complexity constants. By use of the spur reaction model, the Ps yields were correlated to the gas phase reaction between electron acceptors and free electrons, as well as to pulse radiolysis data.