1. Faculty of Engineering and Resource Science, Akita University, 1-1 Tegata Gakuen-cho, Akita 010-8502, Japan
2. Cyclotron Research Center, Iwate Medical University, 348-58 Tomegamori, Takizawa 020-0173, Japan
3. Hyogo University of Teacher Education, 942-1 Shimokume Yashiro-cho Kato-gun, Hyogo 673-1494, Japan