Atomic Photoelectric Effect Above 10 keV

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.

Comparison of theoretical and experimental photoeffect data 0.1 keV to 1.5 MeV

“…1 then pair production which proceeds from a threshold of 1.022 MeV (2 m c 2 ) to dominate over all other processes in the high energy limit.…”

“…Pratt, Ron and Tseng [1] have recently extensively reviewed the existing calculations and measurements of the atomic photoeffect over the range 10 keV to 100 MeV (including material extending down to 1 keV) , complementing an earlier review by Fano and Cooper [2] of theoretical and measured photoeffect data over the range 10 eV to 10 keV.…”

Partial and total dielectronic recombination rate coefficients for W55+to W38+

“…The Rydberg nℓ-values were again calculated for each n up to n = 25 and then on the same n-mesh as used for DR, up to n = 999, with ℓ = 0 − 10, relativistically. At high-T (> 10 9 ) K, many multipoles contribute to the photoionization/recombination at correspondingly high energies [42]. We included up to E40 in CA and E40/M39 in the IC calculations, which is sufficient to converge the total RR rate coefficients to < 1% over the ADAS temperature range.…”

“…In Figure 17 Electric and magnetic multipole radiation contributions to the RR rate coefficients become important at high temperatures [42]. In Figure 23 we have plotted the ionization balance using RR rate coefficients where only electric dipole radiation is included, and using RR rate coefficients where electric and magnetic multipoles up to E40 and M39 have been included.…”

Radial Secondary Electron Dose Profiles and Biological Effects in Light-Ion Beams Based on Analytical and Monte Carlo Calculations using Distorted Wave Cross Sections

“…The photon beams found in radiation transport studies have relatively low photon densities and, as a consequence, only single-photon absorption is observed 1 . To represent the atomic states, we can adopt an independentelectron model, such as the Dirac-Hartree-Fock-Slater self-consistent model (see, e.g., Pratt et al, 1973), in which each electron occupies a single-particle orbital, with welldefined ionisation energy. The set of orbitals with the same principal and total angular momentum quantum numbers and the same parity constitute a shell.…”