1. Shaanxi Engineering Research Center of Controllable Neutron Source, School of Electronic Information, Xijing University, Xi'an 710123, China
2. School of Nuclear Engineering, Xi'an Research Institute of High Technology, Xi'an 710025, China
3. Beijing Research Institute of High Technology, Beijing 100077, China
4. College of Rare Earth and Faculty of Materials Metallurgy and Chemistry, Jiangxi University of Science and Technology, Ganzhou 341000, P. R. China