1. a Department of Material Development , Takasaki Radiation Chemistry Research Establishment, Japan Atomic Energy Research Institute , Watanuki-Machi 1233, Takasaki, Gunma, 370-12, Japan
2. b Department of Chemistry , Faculty of Engineering, Gunma University , Kiryu, Gunma, 376, Japan
3. c Gesellschaft für Schwerionenforschung , Planckstraβe 1, D-6100, Darmstadt 11, Germany