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 deexcitation process. The results show a very distinctive behavior for the H- and He-like heavy systems. In particular, for $K\to L$ 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.

• Received 18 August 2011

DOI:https://doi.org/10.1103/PhysRevA.84.042710