Positrons as probes of early time processes in radiation chemistry

When energetic positrons are injected into liquids, up to 80% of them ultimately form positronium atoms. Most of the Ps atoms are formed by e+ + e- reaction in the end-of-track spurs. Such a spur contains several ion-electron pairs and the de-energized positron. A simple mechanism is presented. In liquid hydrocarbons an upper limit of the fraction of positrons that form Ps by the Ore mechanism is estimated to be 0.1. The data are ready for the development of a stochastic multipair spur model. The model would also apply to conventional radiolysis systems. (author)