- Marek Pfützner, the University of Warsaw, Poland
In the nuclear electron capture (EC) decay sometimes, with a probability of about 10-4, a photon is emitted together with an electron neutrino. Such a process is called radiative electron capture (REC). Our Warsaw group has been investigating this phenomenon over many years, focusing, in particular, on forbidden transitions. These studies revealed a strong disagreement of measured spectra with theoretical models. This was especially puzzling in the case of first-forbidden unique (1u) decays, where the observed gamma spectrum should be determined solely by quantum electrodynamics, as the nuclear matrix elements cancel out. A few years ago, a new theoretical description succeeded to finally solve the REC puzzle for the decays of 1u type. Recently, we hextended this model also to second forbidden nonunique (2nu) decays, and we applied it to the case of 59Ni, measured a long time ago. The result was surprising. It yielded the first evidence for a virtual beta-gamma transition. A possibility for such a virtual decay path had been predicted in the sixties, but all attempts to observe it were unsuccessful. The present identification of this phenomenon was possible due to the new, correct theoretical description of the radiative EC decays. In my talk, I will present a long path leading us to the understanding of this basic nuclear process.
Refreshments will be served at 2:40 PM.