1. Nuclear Science and Engineering Center, Japan Atomic Energy Agency 1 , 2-4 Shirakata, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan
2. Institute for Quantum Life Science, National Institutes for Quantum Science and Technology 2 , 4-9-1 Anagawa, Inage-ku, Chiba-shi 263-8555, Japan