Effect on X-Ray Fine Structure of Deviations from a Coulomb Field near the Nucleus

Deviations from a Coulomb field near the nucleus of very heavy atoms appear to produce changes as large as about one part in 400 on the fine structure splitting of the $2p$ electronic level. Theoretical evaluation of these changes is discussed and available x-ray data analyzed to yield an experimental determination of their magnitude. A nuclear radius as large as $2\times {10}^{-13\mathrm{}}{A}^{\frac{1}{3}}$ cm must be assumed if the observed effects come only from deviations in the Coulomb field due to the finite nuclear size. The preferred interpretation is that most of the contribution to the observed change in fine structure comes from quantum electrodynamic effects (Lamb shift) which produce deviations from a Coulomb field near the nucleus. This appears to provide a method for study of the Lamb shift for large $Z$ and possibly also of nuclear size.