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Hirade, Tetsuya; Suzuki, Naoki*; Saito, Fuminori*; Hyodo, Toshio*
Physica Status Solidi (C), 4(10), p.3714 - 3717, 2007/09
Times Cited Count：6 Percentile：82.43(Physics, Atomic, Molecular & Chemical)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 
-rays. In this work the 
parameter curves measured with trapped electrons and no trapped electrons in polyethylene are interpreted by introducing possible positron reactions. Positrons that escape from Ps formation by the Ore and the spur processes have chance to form Ps with trapped electrons. This Ps formation competes with the positron localization resulting from the trapping between molecules or the weakly binding on molecules, ions, or radicals. Assuming the possibility of both the delayed Ps formation and delayed positron trapping and that S-parameters for ortho-Ps and free positrons are the same, we obtain a good fit to the observed time dependent S-parameter curves .
Suzuki, Naoki*; Hirade, Tetsuya; Saito, Fuminori*; Hyodo, Toshio*
Radiation Physics and Chemistry, 68(3-4), p.647 - 649, 2003/10
Times Cited Count：23 Percentile：80.7(Chemistry, Physical)no abstracts in English
Hirade, Tetsuya; Suzuki, Naoki*; Saito, Fuminori*; Hyodo, Toshio*
no journal, ,
The electrons formed by ionization can be localized with 0.5-3eV at low temperatures (below -50
C) 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.
