Positrons from heavy ion collisions

With the UNILAC heavy ion accelerator at the GSI in Darmstadt 23γU ions can be made to approach 23γU atoms to distances of less than 20 fm. Thus, inner shell electrons experience for a short time the Coulomb field of the combined nuclear charge of 184. Strong relativistic effects are expected to occur in these superheavy quasimolecular systems. Amongst these is a very strong localization of the 1s(sub sigma) and continuum wave functions with a high probability of inner shell vacancy formation. In such circumstances the 1s(sub sigma) state is strongly bound and these inner shell vacancies can be filled either by X-ray emission from bound orbitals, or with electrons from the negative energy continuum. In the latter case positrons are emitted. In a series of experiments positron creation has been investigated. Special care was taken to eliminate background positrons from nuclear excitation. It is established that a dominant fraction of the observed positron yield arises from non nuclear origins. (Auth.)