Frankfurt 2014 – wissenschaftliches Programm
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HK: Fachverband Physik der Hadronen und Kerne
HK 31: Struktur und Dynamik von Kernen
HK 31.2: Gruppenbericht
Mittwoch, 19. März 2014, 17:00–17:30, HZ 4
Isospin properties of low-lying electric dipole excitations — •Vera Derya1, Janis Endres1, Muhsin N. Harakeh2,3, Deniz Savran4,5, Mark Spieker1, Heinrich J. Wörtche2, and Andreas Zilges1 — 1Institute for Nuclear Physics, University of Cologne — 2KVI, University of Groningen, The Netherlands — 3GANIL, CEA/DSM-CNRS/IN2P3, Caen, France — 4ExtreMe Matter Institute EMMI and Research Division, GSI, Darmstadt — 5Frankfurt Institute for Advanced Studies FIAS, Frankfurt
An accumulation of low-lying electric dipole excitations, the electric Pygmy Dipole Resonance (PDR), was observed below and around the neutron threshold in neutron-rich atomic nuclei [1]. In a systematic study, complementary to real-photon scattering experiments, the isoscalar probe of α particles at 136 MeV was used in α-γ coincidence experiments at the Big-Bite Spectrometer at KVI to study the isospin character of low-lying E1 excitations. The combined results permit a separation of the isovector from the isoscalar dipole response. Whereas a splitting into a lower-energy isospin-mixed part and a higher-energy isovector part was observed in heavier nuclei, a state-to-state change in isospin character was found in 48Ca. Recently, protons at 80 MeV were used as an additional probe in a p-γ coincidence experiment. The most recent results and an overview of the systematics will be presented.
Supported by the DFG (ZI 510/4-2), EURONS, and the Alliance Program of the Helmholtz Association (HA216/EMMI).
[1] D. Savran, T. Aumann, and A. Zilges, Prog. Part. Nucl. Phys. 70 (2013) 210.