Investigation of the Pygmy Dipole Resonance in image coincidence experiments Original Research Article

We report on first results from experiments using the (α,α′γ) reaction at Eα=136 MeV to investigate bound electric dipole (E1) excitations building the so-called Pygmy Dipole Resonance (PDR) in the semi-magic nucleus 140Ce. The method of (α,α′γ) allows the separation of E1 excitations from states of higher multipolarity, provides an excellent energy resolution and therefore allows a detailed analysis for each single state. Studying bound E1 excitations in α-scattering experiments at intermediate energies becomes feasible for the first time even in nuclei with a high level density. The surprising results of the first experiment on 140Ce point to a splitting of the PDR in this nucleus.