Fine-structure effect in the relativistic (e,2e) process

Using a transversely polarized electron beam a relativistic (e,2e) experiment has been performed to look for a spin-up-spin-down asymmetry in the electron-impact ionization process caused by the fine-structure effect. An incident energy of 300 keV, coplanar asymmetric kinematics, and the 2p_3/2 shell of uranium (Z=92) have been used. We found clear evidence for the fine-structure effect in the relativistic regime and a qualitative agreement with theoretical results of the relativistic distorted-wave Born approximation, including a change of sign in the angular distribution of the asymmetry near the Bethe ridge.