Second Born approximation for relativistic electron capture: Exact Monte Carlo calculations forC6+-Au andAr18+-Ag collisions

The second-order Oppenheimer-Brinkman-Kramers approximation for relativistic electron capture is formulated, and rigorously calculated K-K cross sections are presented for the first time. Theoretical cross sections for electron capture in collisions of ${\mathrm{C}}^{6+}$-Au at 400 MeV/u and ${\mathrm{Ar}}^{18+}$-Ag at 400 and 1050 MeV/u projectile energy are compared with the experimental data and other approximate second Born results. It is shown that exact second Born cross sections grossly overestimate the experimental data.