Calculation of anomalous scattering for ions and atoms

The anomalous scattering factors g' , g" for forward scattering are generated for neutral Ne and for Ne 2+, 4+, 6+ and 7+ ions, utilizing a dispersion relation integration method, for photon energies from 1 to 70 keV. Photoionization cross sections (i.e., g" ) above threshold are calculated in the relativistic Hartree-Slater potential; the code of Cromer and Liberman [1] is used to obtained the corresponding bound-free contribution to g' from g" . However it is found that the contribution from bound-bound transitions to g' is much more important for ions than for the neutral atom. The primary reason is that in ions there are more inner-shell vacancies for which bound-bound transitions are allowed. Near the K threshold the major bound-bound transition for the neutral neon atom is 1 s → 3 p , whose oscillator strength is about ten times less than that of 1 s → 2 p transition which is allowed in neon ions. With the contribution from the major bound-bound transitions included in g' , the Rayleigh scattering cross sections obtained in this way agree well with results of direct S-matrix calculations [2].