1. Japan Atomic Energy Research Institute, Tokai Research Establishment, Shirakata, Tokai-mura Naka-gun, Ibaraki 319-1195, Japan
2. Japan Atomic Energy Research Institute, Takasaki Radiation Chemistry Research Establishment Watanuki-machi, Takasaki-shi, Gunma 370-1292, Japan
3. Matsushita Industrial Equipment Co., Ltd., Inazu-cho, Toyonaka-shi, Osaka 561-0854, Japan