Pygmy Dipole Strength and Neutron Skins in Exotic Nuclei

Journal Article · Mon May 12 04:00:00 EDT 2008 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.2939304· OSTI ID:21143355

Klimkiewicz, A; Adrich, P ^[1]; Paar, N; Vretenar, D ^[2]; Fallot, M; Boretzky, K; Aumann, T; Pramanik, U Datta; Emling, H; Geissel, H; Hellstroem, M; Jones, K L; Simon, H; Suemmerer, K ^[1]; Cortina-Gil, D ^[3]; Elze, Th W; Palit, R ^[4]; Kratz, J V; Nociforo, C ^[5]; Kulessa, R ^[6]

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1. Gesellschaft fuer Schwerionenforschung, D-64291 Darmstadt (Germany)
2. Physics Department, Faculty of Science, Univers. of Zagreb, Bijenicka 32, 10000 Zagreb (Croatia)
3. Universidad de Santiago de Compostela, 15706, Santiago de Compostela (Spain)
4. Institut fuer Kernphysik, Johann Wolfgang Goethe-Universitat, D-60486 Frankfurt am Main (Germany)
5. Institut fuer Kernchemie, Johannes Gutenberg-Universitat, D-55099 Mainz (Germany)
6. Instytut Fizyki, Uniwersytet Jagiellonski, PL-30-059 Krakow (Poland)

Dipole strength distributions were determined for the neutron-rich nuclei {sup 129-132}Sn and {sup 133,134}Sb from electromagnetic excitation in an experiment using the FRS-LAND setup. For all nuclei, a sizeable fraction of ''pygmy'' dipole strength at excitation energies well below the giant dipole resonance was observed. The integrated low-lying dipole strength of the nuclei with low neutron separation energies can be compared to results for stable nuclei (e.g. N = 82 isotopes) determined for the energy regime of 5-9 MeV. A clear increase of the dipole strength with increasing asymmetry of the nuclei is observed. Comparing the ratio of the low-lying dipole over the giant dipole strength to recent relativistic mean field calculations, values for the parameters a{sub 4} and p{sub 0} of the symmetry energy and for the neutron skin thickness are derived. Averaged over {sup 130}Sn and {sup 132}Sn we extract a-bar{sub 4} = 31.8{+-}1.3 MeV and p-bar{sub 0} = 2.2{+-}0.5 MeV/fm{sup 3}. The neutron skin sizes are determined to R{sub n}-R{sub p} = 0.23{+-}0.03 fm and 0.24{+-}0.03 fm for {sup 130}Sn and {sup 132}Sn, respectively. For {sup 208}Pb a neutron skin thickness of R{sub n}-R{sub p} = 0.18{+-}0.035 fm follows, when applying the same method and using earlier published experimental findings on the dipole strength.

• OSTI ID: 21143355
• Journal Information: AIP Conference Proceedings, Journal Name: AIP Conference Proceedings Journal Issue: 1 Vol. 1012; ISSN APCPCS; ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ANTIMONY 133
ANTIMONY 134
ANTIPROTONS
DIPOLES
EXCITATION
GIANT RESONANCE
LEAD 208
MEAN-FIELD THEORY
MEV RANGE
NEUTRON SEPARATION ENERGY
NEUTRON-RICH ISOTOPES
NEUTRONS
NUCLEAR STRUCTURE
RELATIVISTIC RANGE
STRENGTH FUNCTIONS
TIN 129
TIN 130
TIN 132