1. Isotope Imaging Laboratory, CRIS; Hokkaido University; Sapporo 001-0021 Japan
2. Department of Physics; Osaka University; Toyonaka 560-0043 Japan
3. Graduate School of Engineering Sciences; Kyushu University; Kasuga 816-8580 Japan
4. JEOL Ltd.; Akishima 196-8558 Japan
5. Department of Natural History Sciences; Hokkaido University; Sapporo 060-0810 Japan