Gärtner, P; Heinz, U; Müller, B; Greiner, W, *Limiting charge for electrostatic point sources*, vol. 300 no. 2-3
(1981),
pp. 143-155 [doi] .
**Abstract:**

*We investigate the behaviour of the vacuum charge around a supercritical nucleus with Z>137 in dependence on the nuclear radius. The screening effects are considered in a quasiclassical approximation. We show that in the point nucleus limit the nuclear charge is screened by the vacuum charge up to Z=137. This means that the coupling strength of a point charge in QED cannot be larger than 1. The influence of the heavier leptons is also discussed. © 1981 Springer-Verlag.*