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Komuro, Yo; Hirade, Tetsuya; Suzuki, Ryoichi*; Odaira, Toshiyuki*; Muramatsu, Makoto*
Radiation Physics and Chemistry, 76(2), p.330 - 332, 2007/02
Times Cited Count：3 Percentile：25.51(Chemistry, Physical)Recently, positronium (Ps) formation mechanism in the spur is becoming clarified. Blob model, the modified Spur model, proposed by Stepanov can give information of Ps formation time. Dauwe et al. showed that S(t) curve of PMMA observed by AMOC measurement could be fitted by the blob model. The young-age broadening was found and explained with the delayed slowing down of Ps by Stuttgart group. The delayed Ps formation was shown by Suzuki et al. especially at low temperatures, because positrons can diffuse long distance to find trapped electrons. According to the blob model, Ps formation even after long diffusion of positrons might be possible even at the room temperature. Now we are trying to obtain the experimental evidence of delayed Ps formation in spur process.
Komuro, Yo; Hirade, Tetsuya; Suzuki, Ryoichi*; Odaira, Toshiyuki*; Muramatsu, Makoto*
no journal, ,
The annihilation 
rays from the para-pojitoronium (p-Ps) state gives narrower Doppler broadening. The broader Doppler broadening was observed at very young age region that is mainly from the annihilation process of p-Ps. It was explained by the delayed Ps slowing down and the delayed Ps formation. We have successfully obtained the experimental evidence of the delayed Ps formation.
Komuro, Yo; Hirade, Tetsuya; Suzuki, Ryoichi*; Odaira, Toshiyuki*; Muramatsu, Makoto*; Suzuki, Takenori*
no journal, ,
Many ions and the excess electrons are formed by the injected positron just before the thermalization of that positron in a small area (it is called spur or blob) in condensed matter. The positron has a chance to form positronium (Ps) with one of the excess electrons. According to the model of Ps formation in the spur (blob), the initial encounter pairs of an electron and a positron will form Ps in short time. Some of the positrons have some possibility to form Ps after diffusion in several hundreds pico-seconds. There were experimental results that were interpreted as a Ps thermalization by a group in Germany more than 10 years ago. However, we have believed that some of the results were caused by the delayed Ps formation and have successfully obtained the experimental evidence of the delayed Ps formation by applying electric fields on the sample, fused quartz.
Komuro, Yo; Hirade, Tetsuya; Suzuki, Ryoichi*; Odaira, Toshiyuki*; Muramatsu, Makoto*; Suzuki, Takenori*
no journal, ,
The injected positrons to condensed materials form a very small area where they deposit much energy and some tens of ion-electron pairs are formed. This area is called a positron spur or blob. Positrons have a possibility to form positronium at this area. Some of the positrons are isolated from the excess electrons when they thermalized. They will have smaller possibility to form positronium and longer time to form positronium. Therefore the positronium formation by the isolated positrons from excess electrons can be easily inhibited by applying the external electric fields. We have found this expected phenomena by applying the external electric fields.
