Positron production in collision of heavy nuclei
  We consider the electromagnetic production of positron in collision of heavy nuclei, with the simultaneously produced electron captured by one of the nuclei. This cross-section exceeds by about four orders of magnitude the cross-section of $e^+ e^-$ production. 
I.B. Khriplovich and D.A. Solovyev
nucl-th hep-ph physics.atom-ph