München 2006 – wissenschaftliches Programm
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HK: Physik der Hadronen und Kerne
HK 35: Kernphysik/Spektroskopie
HK 35.3: Vortrag
Mittwoch, 22. März 2006, 17:30–17:45, C
Theory of Pygmy Dipole Resonances in Exotic Nuclei — •Nadia Tsoneva and Horst Lenske — Institut für Theoretische Physik, Universität Giessen, Germany
The possible connection between neutron skins and low-energy dipole excitations is investigated. For this purpose, a method incorporating both HFB and multi-phonon QPM theory was developed [1]. The mean field parameters can be determined self-consistently for every nucleus under consideration. The evolution of the dipole strength with the neutron excess for the Z=50 isotopic chain and N=82 isotones is investigated. From QRPA and QPM calculations a low-energy dipole strength concentrated in the energy region Ex∼ 6−8 MeV is obtained. The calculations are compared to recent data from photon scattering experiments. The analysis of the corresponding neutron and proton transition densities indicates almost pure neutron oscillations at the nuclear surface such that a PDR can be identified. The dependence of the PDR properties on the neutron excess has been investigated. A close correlation between the total PDR strength and the size of the neutron skin could be identified [1]. An interesting point was to explain the PDR behaviour in nuclei close to the transition from a neutron to a proton skin, e.g. 100Sn-110Sn, possibly transforming the neutron PDR mode into a proton. An important step in the understanding of the dipole spectra is to disentangle the PDR states from the low-energy two-phonon dipole states. This is achieved by using the QPM approach with up to three-phonon configurations. Supported by DFG, project Le 439/2-5.
[1] N. Tsoneva, H. Lenske, Ch. Stoyanov, Phys. Lett. B 586 (2004) 213.