Positrons from quasimolecular states give data on QED

With the availability of lead and uranium beams at the new heavy‐ion accelerator in Darmstadt, West Germany, it has become possible to study very strongly bound quasimolecular states formed transiently by the combined charges of projectile and target nuclei during atomic collisions. In collision systems such as uranium with uranium, provided the two nuclei approach each other close enough, one is able to explore quantum‐electrodynamic phenomena for the first time under conditions where the electromagnetic coupling to the nucleus is large $(Zα≳1).$