1. Tohoku University, Cyclotron and Radioisotope Center, Aramaki, Aoba-ku, Sendai 980, Japan
2. Japan Atomic Energy Research Institute, Department of Nuclear Reactor Engineering Tokai, Ibaragi 319-11, Japan
3. Japan Atomic Energy Research Institute, Takasaki Establishment Watanuki-cho, Takasaki, Gunma 370-12, Japan
4. Kyoto University, Department of Nuclear Engineering, Yoshida, Sakyo-ku, Kyoto 606, Japan
5. Tohoku University, Department of Nuclear Engineering, Aramaki, Aoba-ku, Sendai 980, Japan