1. Research Reactor Institute, Kyoto University Kumatori-cho, Sennan-gun, Osaka 590-04, Japan
2. Kyoto University, Department of Nuclear Engineering Yoshida-honmachi, Sakyo-ku, Kyoto 606-01, Japan
3. Japan Atomic Energy Research Institute, Department of Radioisotopes Tokai-mura, Naka-gun, Ibaraki 319-11, Japan