1. a Takasaki Radiation Chemistry Research Establishment, JAERI , 1233 Watanuki-machi, Takasaki, Gunma, 370-12, Japan
2. c Hahn-Meitner-Institute , Glienickerstr. 100, D-14109, Berlin, 39, Germany
3. b Instituto de Fisica, Universidade Federal do Rio Grande do Sul , Campus do Vale, 90.049, Porto Alegre, RS, Brasil