Dipole excitations via isoscalar probes: The splitting of the pygmy dipole resonance in 124Sn

Inelastic α-scattering excitation cross sections are calculated for electric-dipole excitations in 124Sn based on the transition densities obtained from the relativistic quasiparticle time-blocking approximation (RQTBA) in the framework of a semiclassical model. The calculation provides the missing link to directly compare the results from the microscopic RQTBA calculations to recent experimental data measured via the (α,α′γ) reaction, which show a structural splitting of the low-lying E1 strength often denoted as pygmy dipole resonance (PDR). The experimentally observed splitting is reproduced by the cross-section calculations, which allows us to draw conclusion on the structure of the PDR.