Reactions of free positrons in low temperature polyethylene: delayed Ps formation and positron localization

Abstract Positronium (Ps) can be formed by a reaction of trapped electrons and free positrons at low temperatures in molecular solids. While Ps formation by Ore and spur process must be fast, Ps formation by trapped electrons and free positrons is possible even at later positron age. The evidence of this delayed Ps formation was obtained by age‐momentum correlation measurement of electron‐positron pair annihilation γ‐rays. In this work the S (t) parameter curves measured with trapped electrons and no trapped electrons in polyethylene are interpreted by introducing possible positron reactions. It is quite natural to believe that the delayed Ps formation competes with the positron localization. We have successfully obtained a good simultaneous fit to the observed time dependent S‐parameter curves, S (t), with and without the trapped electrons in the sample. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)