1. Department of Applied Physics, National Defense Academy of Japan, Yokosuka, Kanagawa, Japan
2. National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan
3. Fuji Electric Company Ltd., Hino, Tokyo, Japan
4. Cyclotron and Radioisotope Center, Tohoku University, Sendai, Miyagi, Japan