Theory of positron creation in supercritical quasimolecules

Collisions of very heavy ions at energies close to the Coulomb barrier are discussed as a unique tool to study the behaviour of the electron-positron field in the presence of strong external electromagnetic fields. Theoretical predictions for positron production rates are compared with experimental results. Emphasis is laid on effects due to nuclear time delay and on the influence of electron screening for both sub- and supercritical collision systems. Internal electron-positron pair production from electric monopole transitions is investigated for atoms with charge number up to Z approx. = 170