Recent considerations on the GSI positron peaks

In collisions of very heavy ions superheavy quasiatoms are created in which the electrons experience the combined electric field of the projectile and target nucleus. In these exotic systems the strongest bound 1s-state enters as a resonance the negative energy continuum provided the total nuclear charge number exceeds the critical value of Zcr = 173. This peculiar fact leads to a fundamentally new decay channel for a K-shell vacancy, which gives rise to spontaneous positron emission. The verification of this fascinating process constituted one basic motivation for the experimental research on positron production in heavy-ion collisions