No abstract

The current understanding of the theory of the atomic photoelectric eGect 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 photoe6ect 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 mdving in a relativistic Hartree -Pock -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 photoefl'ect matrix element are of the order of an electron Compton wave length. This leads to the predictions that the photoeffect cross section in a-sere|:ned 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 ditfer 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.

Phys. Rev. 167, 17 (1968).As an example of this form of wave function used in ion-atom charge transfer reactions see D. F. Gallaher and L. Wilets, Phys. Rev. 169, 139 {1968).A discussion of relativistic bremsstrahlung cross sections is given for incident-electron kinetic energies in the range 5 keV--1 MeV, based on an exact numerical calculation using screened potentials. Comparisons are made with previous authors' results, extending the discussion of a preliminary note. Exact point-Coulomb and Born-approximation results are contrasted. The present results show that the Born approximation significantly underestimates the bremsstrahlung cross sections in the energy region considered. Screening effects are somewhat larger than expected, and when large are not well described by a form factor.

No abstract

No abstract

No abstract

Analytic expressions for bremsstrahlung spectra from neutral atoms and ions, including the polarizational bremsstrahlung contribution in a stripped atom approximation, are developed for electron scattering at energies of 10-2000 keV. A modified Elwert factor and a simple higher Born correction are used for the Coulomb spectrum, with ordinary bremsstrahlung screening effects in ions and atoms adequately characterized in the non-relativistic Born approximation. In parallel with the development of this analytic description, new numerical results are obtained for ordinary bremsstrahlung from ions and from bare nuclei, appreciably extending the available data set which can be used to study dependences on element, ionicity, energy and the fraction of incident energy radiated. The accuracy of predictions with the analytic expressions is then determined by comparison with the full numerical relativistic partial-wave results for ordinary bremsstrahlung and with non-relativistic numerical results in the Born approximation or in partial waves for the polarizational amplitude.

No abstract