Second-order Born calculations for electron capture in relativistic U+U collisions

Using an exact evaluation of the relativistic second-order Oppenheimer-Brinkman-Kramers approximation, total and differential cross sections for electron capture in ${\mathrm{U}}^{92+}$+${\mathrm{U}}^{91+}$ collisions are calculated for projectile energies between 0.5 and 100 GeV/u. It is shown that (a) at 100 GeV/u the asymptotic cross-section behavior is not yet reached, (b) spin-flip transitions and negative-energy intermediate states become important at high energies, and (c) the Thomas peak in the differential cross section is relativistically suppressed.