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ISBN 978-3-86853-786-4

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978-3-86853-786-4, Reihe Physik

Janis Endres
Systematic studies of the Pygmy Dipole Resonance with hadronic and electromagnetic probes

102 Seiten, Dissertation Universität Köln (2011), Softcover, A5

Zusammenfassung / Abstract

This thesis presents the systematic study of the Pygmy Dipole Resonance (PDR) in the atomic nuclei 94Mo, 124Sn, and 138Ba using the new method of (α,α′γ) coincidence ex- periments at 34 MeV/nucleon bombarding energy. These experiments provide a deeper insight into the underlying structure of this resonance, since hadronic interaction is dom- inant at the chosen kinematic conditions. The measurements have been performed at the Kernfysisch Versneller Instituut (KVI) in Groningen, The Netherlands. The compar- ison of the obtained results to the dipole strength distribution measured in real photon scattering experiments on the same nuclei reveals a splitting of the PDR into two ener- getically separated parts with different underlying structure. This phenomenon seems to be a general feature of this resonance, since it is so far observed in all studied nuclei.

The details and results of the experiments are presented in this thesis and a comparison to the results of theoretical microscopic calculations is given that allow an interpretation of the experimentally observed splitting of the PDR. It turns out that the energetically lower-lying group of states seemingly belongs to an isoscalar neutron-skin oscillation, while the higher-lying group of dipole transitions seems to belong to a transitional region on the tail of the isovector Giant Dipole Resonance (IVGDR).