1. Muon Science Laboratory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan
2. Muon Science Section, Materials and Life Science Division, J-PARC Center, Tokai, Ibaraki 319-1195, Japan
3. Radioisotope Laboratory, Department of Chemistry, School of Science, The University of Tokyo, Bunkyo, Tokyo 113-0033, Japan