EXACT 2ND-ORDER BORN CALCULATIONS FOR RELATIVISTIC ELECTRON-CAPTURE

Second-order Born cross sections for electron capture in relativistic collisions have been calculated without further approximations for a large number of projectile-target combinations and energies. Within the regime of high-Z target atoms and energies of a few GeV/u, the exactly evaluated cross sections are considerably larger than first-order cross sections, which already overestimate the experimental results. This shows that the Born expansion is not a suitable perturbation series in the charge and energy regime considered. At the same time it is demonstrated that previous evaluations using peaking approximations and alpha-Z expansions are in error by more than an order of magnitude. For p + H collisions the differential cross section exhibits a peak at the classical relativistic Thomas angle.