1. Frontiers Science Center for Rare Isotopes, Lanzhou University, Lanzhou 730000, P. R. China
2. School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, P. R. China
3. China Institute for Radiation Protection, Taiyuan 030000, P. R. China
4. Laboratory of Ion Beam Physics, ETH Zurich, Zurich 8093, Switzerland