| Co-Investigator(Kenkyū-buntansha) |
OKI Yuichi Radiation Science Center, High Energy Accelerator Research Organization, Research Associate, 放射線科学センター, 助手 (40204094)
MIURA Taichi Radiation Science Center, High Energy Accelerator Research Organization, Research Associate, 放射線科学センター, 助手 (80209717)
SUZUKI Takenori Radiation Science Center, High Energy Accelerator Research Organization, Professor, 放射線科学センター, 教授 (40162961)
NUMAJIRI Masaharu Radiation Science Center, High Energy Accelerator Research Organization, Research Associate, 放射線科学センター, 助手 (20189385)
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| Research Abstract |
The positron-irradiation effect has been studied and increases and decreases in the positronium (Ps) formation have been reported at low and room temperature, respectively. Before observing positronium (Ps) quenching by irradiating polymer samples with visible light, the increase at low temperature was explained by the relaxation behavior of polymer structures. A quenching experiment has demonstrated that Ps formation is accelerated by an increase in the trapped electrons, which are induced by the ionization of injected positrons and trapped in a shallow potential being formed among polymer structures at low temperature. This is a similar phenomenon to the well-known "anti-inhibition or anti-recombination effect"
The decrease in I_3 at room temperature has been explained by many ideas, such as cross-links, structure change, and radicals. A structure change and the cross-links were introduced to explain the decrease in I_3 at low gamma-irradiation doses of around 10 kGy, since, at a low
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irradiation dose, it seems to be difficult to expect radicals which affect the change of I_3.
Although positron annihilation lifetime spectroscopy (PALS) is a useful method for studying the characteristics of polymers, all factors, which affect Ps formation, must be paid attention to in order to understand the result. From this point of view, the complicated feature of I_3 is worth to be investigated and the study may have a potential to increase the validity of PALS as the analytical method of polymers.
In this research, the radiation effect induced in samples by positrons has been discussed. Positrons are supplied as a probe from positron sources and at the same time induce radiation effect in the samples. From this point of view PA is not an un-destructive method for polymer. It has been shown that, using the idea of trapped electrons, relaxation process of polymer structures can be investigated by PALS as a secondary effect of the disappearance of the shallow potential due to the thermal molecular motion. Less
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