Atomic Photoelectric Effect Above 10 keV

The current understanding of the theory of the atomic photoelectric effect is reviewed for incident photon energies above 10 keV, complementing the earlier review of Fano and Cooper (1968) at lower energies. The theoretical developments of the last two decades are of two types: (1) analytic results giving insight into many aspects of the photoelectric process and (2) exact numerical cross sections calculated with high speed electronic computers. The basic assumptions underlying the photoeffect calculations are described, and pertinent atomic models are discussed. In the energy range considered, satisfactory results are obtained with the process described as the ejection of an electron moving in a relativistic Hartree-Fock-Slater potential. Exchange, correlation, and other effects are discussed. Many features of the process can be understood with the realization that the important regions in configuration space in the photoeffect matrix element are of the order of an electron Compton wave length. This leads to the predictions that the photoeffect cross section in a screened potential can be obtained from a point-Coulomb result by a simple normalization, that angular distribution shapes and polarization correlations are the same in the two cases, and that results for photoeffect from different subshells of the same angular momentum are similarly related. The numerical methods, achieving total cross sections accurate to 1%, are described and compared with experiment. Different self-consistent atomic models yield cross sections which differ by 3%-8%; these agree with experiments of similar accuracy. New and more accurate cross section tabulations that have recently become available are discussed and recommendations are made concerning their use.