Angular Distribution of Relativistic AtomicK-Shell Photoelectrons

Using the high-energy limit of the exact Coulomb wave function for the outgoing electron, the differential cross section, correct to three orders in $\alpha Z$, is calculated for the $K$-shell photoeffect. An analytic expression, exact in $\alpha Z$, is obtained for the differential cross section for the special case in which the electron emerges in the forward direction.