1. Materials Sciences Research Center, Japan Atomic Energy Agency, Tokai-mura 319-1195, Ibaraki, Japan
2. J-PARC Center, Japan Atomic Energy Agency, Tokai-mura 319-1195, Ibaraki, Japan
3. Division of Biophysics, Department of Physiology, Jichi Medical University, Shimotsuke 329-0498, Tochigi, Japan