1. Institute of Modern Physics, Shanxi Normal University, Taiyuan 030031, P. R. China
2. Shanxi University of Electronic Science and Technology, Linfen 041000, P. R. China
3. China Institute for Radiation Protection, Taiyuan 030006, P. R. China
4. Radiation Measurement and Dose Assessment, National Institutes for Quantum and Radiological Science and Technology, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan
5. Research Institute of Nuclear Engineering, University of Fukui, Fukui 914-0055, Japan