Using a transversely polarized electron beam a relativistic $\mathrm{}(e,2e)\mathrm{}$ 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 $\mathrm{}(Z=92\mathrm{})\mathrm{}$ 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.

• Received 17 July 1997

DOI:https://doi.org/10.1103/PhysRevA.58.R2638