1. Tritium Technology Group, Directorates of Fusion Energy Research, Japan Atomic Energy Agency, Tokai-mura, Naka-gun, Ibaraki pref. 319-1195 JAPAN
2. Faculty of Science, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka city, Shizuoka 422-8529, JAPAN