1. Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152-8550, Japan, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan, and Department of Chemistry, College of Science and Engineering, Aoyama Gakuin University, Chitosedai, Setagaya-ku, Tokyo 157-8572, Japan