Magnetic Sublevel Population and Alignment for the Excitation of H- and   He-like Uranium in Relativistic Collisions
  We have measured the alignment of the L-shell magnetic-substates following the K-shell excitation of hydrogen- and helium-like uranium in relativistic collisions with a low-Z gaseous target. Within this experiment the population distribution for the L-shell magnetic sublevels has been obtained via an angular differential study of the decay photons associated with the subsequent de-excitation process. The results show a very distinctive behavior for the H- and He-like heavy systems. In particular for $K \rightarrow L$ excitation of He-like uranium, a considerable alignment of the L-shell levels was observed. A comparison of our experimental findings with recent rigorous relativistic predictions provides a good qualitative and a reasonable quantitative agreement, emphasizing the importance of the magnetic-interaction and many-body effects in the strong-field domain of high-Z ions. 
A. Gumberidze, S. Fritzsche, S. Hagmann, C. Kozhuharov, X. Ma, M.   Steck, A. Surzhykov, A. Warczak, Th. St\"ohlker
physics.atom-ph