Polarization of the Lyman-α₁ X-ray line emitted by hydrogen-like Ti²¹⁺, Ar¹⁷⁺, and Fe²⁵⁺ ions excited by electron impact

We present a review of the relativistic convergent close-coupling (RCCC) method and describe how it has been used to resolve the discrepancy between theory and experiment for the polarization of the Lyman-α₁ X-ray line emitted by hydrogen-like Ti²¹⁺, Ar¹⁷⁺, and Fe²⁵⁺ ions excited by electron impact. We find that taking account of Breit relativistic corrections is important to resolve the discrepancy between experiment and theoretical calculations. (author)