1. College of Physics, Sichuan University, Chengdu 610065, China
2. Faculty of Engineering, University of Nottingham, University Park, Nottingham 999020, U.K.
3. School of Automobile and Traffic Engineering, Jiangsu University, Zhenjiang 212013, China
4. Key Laboratory of Radiation Physics and Technology of Ministry of Education, Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610064, China