Inclusion of the Generalized Breit Interaction in Determining Relativistic Cross Sections for Excitation of Highly Charged Ions by Electron Impact.
The inclusion of the Breit interaction as a correction to the Coulomb interaction has been employed in various atomic physics calculations for more than 60 years. The focus of this thesis is the inclusion of the Breit interaction in the scattering matrix elements for calculating electron impact excitation cross sections or collision strengths. It is also intended to determine the range of conditions for which the Breit interaction has a significant effect on these results. The process of excitation has, so far, avoided such a thorough analysis. A review of the theory of relativistic electron impact excitation is provided. The method of calculation is a fully relativistic distorted-wave approach which is equivalent to first-order time-dependent perturbation theory. In this work, the perturbation is taken to be the sum of the Coulomb and Breit interactions between the free and bound electrons. The required bound state wavefunctions and energies are calculated with a relativistic Hartree-Fock -Slater or Dirac-Fock-Slater method. The approximations involved in these two methods require the atomic number of the target ion to be at least twice its number of bound electrons if accurate results are to be obtained. Thus, only highly ionized ions are considered in this work. Collision strengths are presented for H-like, He-like and Li-like ions with atomic numbers Z = 26, 54 and 92. Several kinds of transitions and impact electron energies are also considered. These data indicate that all three forms of the Breit interaction considered in this research can have significant effects on the excitation collision strengths. Effects range from as much as nearly 30% for Z = 54 up to nearly 70% for Z = 92 in transitions involving the tightest bound 1s electron. These large effects are exhibited for the three types of ions listed above and persist over a range of electron energies. It is expected that the present data will be useful to those researchers specializing in high temperature plasma modeling or plasma diagnostics. This data may also be used to compare with and interpret future results of electron beam ion trap experiments.
- Pub Date:
- January 1992
- Physics: Atomic; Physics: Fluid and Plasma