Atomic Photoelectric Effect at High Energies

Total cross sections are obtained for the photoelectric effect from the $K$ shell of an atom of arbitrary charge, in the limit of high energies. An approximate analytic formula then is deduced to cover the entire high-energy region. For heavy elements and very high energies the differences from previous predictions are large. It is noted that these results also apply to other processes, including the one photon annihilation of fast positrons.