1. a Department of Polymer Science Faculty of Science , Osaka University , Toyonaka, Osaka, Japan
2. c Central Research Laboratories, Toyo Rayon Co. Ltd. , Sonoyama, Otsu, Japan
3. b Osaka Laboratories for Radiation Chemistry , Japan Atomic Energy Research Institute Neyagawa , Osaka, Japan
4. d Faculty of Engineering , Hokkaido University , Sapporo, Japan