Positronium formation mechanism of trapped electrons and positrons

Hirade, Tetsuya  ; Suzuki, Naoki*; Saito, Fuminori*; Hyodo, Toshio*

The electrons formed by ionization can be localized with 0.5-3eV at low temperatures (below -50C) in some materials for long time. Positrons injected in liquids and molecular solids have a chance to form positronium with one of the excess electrons in the spur. However some of the positrons can escape from the positronium formation and they will annihilates from free positron state, usually. If there are weakly localized electrons in the materials at low temperatures, positrons will have the next chance to form positronium with these electrons. We showed that this positornium formation was slower than the positoronium formation in the spur. We have analyzed the data with considering the positron localization time and obtained several 10 ps as the localization time of positrons in polyethylene at 20K.