Positron spectra from internal pair conversion observed in 238U + 181Ta collisions

Abstract

Abstract. We present new results from measurements and simulations of positron spectra, originating from 238 U + 181 Ta collisions at beam energies close to the Coulomb barrier. The measurements were performed using an improved experimental setup at the double-Orange spectrometer of GSI. Particular emphasis is put on the signature of positrons from Internal-Pair-Conversion (IPC) processes in the measured e + -energy spectra, following the de-excitation of electromagnetic transitions in the moving Ta

Probing QED Vacuum with Heavy Ions

“…All efforts were ended when improved experiments failed to find peaked positron lines where earlier experiments had seen them [86,87]. The consensus view today is that the earlier intriguing observations were due to highly system dependent nuclear excitations converting into pairs [88].…”

Pair production by Schwinger and Breit–Wheeler processes in bi-frequent fields

“…Besides the mentioned strong (but presently not strong enough) fields, the Coulomb fields accompanying heavy and super-heavy atomic nuclei have also been considered as an option to study the vacuum break down (Rafelski, Fulcher & Greiner 1971;Müller et al 1972;Müller, Rafelski & Greiner 1973;Rafelski, Müller & Greiner 1978;Bialynicki-Birula, Gornicki & Rafelski 1991). Previous experiments, however, have not been conclusive (Heinz et al 2000).…”