1. Division of Global Environmental Science and Engineering, Graduate School of Natural Science and Technology, and Institute of Nature and Environmental Technology, Kanazawa University, Kakuma, Kanazawa, Ishikawa 920-1192, Japan, and Japan Atomic Energy Research Institute (JAERI), 2-4, Shirakata Shirane, Tokai-muta, Naka-gun, Ibaraki 319-1195, Japan