Fully relativistic calculations of and fits to 1sionization cross sections

The range of conditions for which inclusion of the generalized Breit interaction is important in calculating the scattering matrix elements for 1s ionization is explored within the relativistic distorted-wave approximation. This approach is applied to the calculation of 1s ionization cross sections for a variety of ions with one to four bound electrons and nuclear charge Z in the range of $10<~Z<~92.$ These data are then interpolated with simple, but accurate, fit formulas. The resulting expressions are readily integrated over a relativistic Maxwellian electron distribution function to obtain rate coefficients for plasma modeling. A discussion of the high energy behavior of the cross sections for large Z is also given.