1. Institute of Atomic and Molecular Physics; Sichuan University; Chengdu 610065 P.R. China
2. Department of Physics; Taiyuan Normal University; Taiyuan 030031 P.R. China
3. Key Laboratory of High Energy Density Physics and Technology of Ministry of Education; Sichuan University; Chengdu 610064 P.R. China
4. Key Laboratory of Neutron Physics; Institute of Nuclear Physics and Chemistry; China Academy of Engineering Physics; Mianyang 621900 P.R. China