Resonance structure of the Gamow-Teller (GT) and first-forbidden (FF) β+/EC decay strength functions

The experimental measurement data on the fine structure of Sβ(E) in spherical and deformed nuclei are analyzed. Modern nuclear spectroscopy methods allowed the split of the peaks caused by nuclear deformation to be revealed in Sβ(E) for transitions of the Gamow- Teller (GT) type. The resonance nature of Sβ(E) for first-forbidden (FF) transitions in both spherical and deformed nuclei is experimentally proved. It is shown that at some nuclear excitation energies FF transitions can be comparable in intensity with GT transitions.