1. Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, O-okayama, 2-12-1, Meguro-ku, Tokyo 152-8550, Japan
2. Present address: Faculty of Science and Technology, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554, Japan (Professor Emeritus of Tokyo Institute of Technology)
3. Present address: Nippon Micrometal Corporation, Sayamagahara 158-1, Iruma-shi, Saitama 358-0032, Japan