1. Natural History Sciences, Isotope Imaging Laboratory; Hokkaido University; Sapporo Hokkaido 001-0021 Japan
2. JEOL Ltd., Musashino; Akishima Tokyo 196-8558 Japan
3. Department of Physics; Osaka University; Toyonaka Osaka 560-0043 Japan
4. Graduate School of Engineering Sciences; Kyushu University; Kasuga Fukuoka 816-8580 Japan
5. Institute of Space and Astronautical Science; Japan Aerospace Exploration Agency; Sagamihara Kanagawa 252-0222 Japan