Dipole excitations via isoscalar probes: The splitting of the pygmy dipole resonance in124Sn

Abstract

Inelastic $\ensuremath{\alpha}$-scattering excitation cross sections are calculated for electric-dipole excitations in ${}^{124}\mathrm{Sn}$ 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 $(\ensuremath{\alpha},{\ensuremath{\alpha}}^{\ensuremath{'}}\ensuremath{\gamma})$ 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.