Splitting of the Pygmy Dipole Resonance

Abstract

Abstract.We report on experiments using the (α, α γ) method to investigate the structure of the Pygmy Dipole Resonance (PDR) in the nuclei 94 Mo, 124 Sn, 138 Ba and 140 Ce. The experiments were performed with the Big-Bite Spectrometer (BBS) at the KVI at an incident energy of Eα = 136 MeV. The method allows a clean separation of the PDR from other excitations in the same energy region by selecting the ground-state γ-decay channel. In addition, the high resolution of the γ-ray spectroscopy using high-purity Germanium detectors allows a state-tostate analysis even in the case of the rather high level density of the investigated nuclei. The comparison to (γ, γ ) experiments on the same nuclei reveals a splitting of the PDR into two groups of states with different underlying structure.