Berlin 2005 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 3: Kernphysik/Spektroskopie

HK 3.1: Group Report

Friday, March 4, 2005, 14:00–14:30, TU MA004

Observation of soft and giant dipole modes in ¹³²Sn and neighboring unstable nuclei — •Adam Klimkiewicz — GSI, Darmstadt, Germany

Secondary beams of unstable neutron-rich ^129−132Sn, ^132−135Sb and ^136,137Te isotopes (∼500 MeV/u) were produced by in-flight fission of a primary ²³⁸U beam at GSI, Darmstadt. Dipole strength distributions ranging from the neutron threshold up to 30 MeV excitation energy were derived from the measured electromagnetic excitation cross sections in a Pb target using the LAND setup at the fragment separator FRS.

The data reveal the giant dipole resonance structure. In addition, in some of the isotopes, clear evidence for a resonant-like, relatively narrow structure at lower excitation energy is obtained. In ¹³²Sn this low-lying resonance is centered at 10 MeV and comprises 4(2) % of the TRK sum rule. The systematics of the parameters of low-lying and giant dipole resonances will be presented. The low-lying resonance will be discussed with regard to soft dipole modes expected to arise from a neutron skin vibration against the nucleus core, see also earlier photoabsorption measurements on stable N=82 nuclei [1]. The data are compared to (Q)RPA calculations [2,3] and the impact on r-process nucleosynthesis calculations is briefly addressed [4].

Work supported by BMBF and GSI.

[1] A.Zilges et al., Phys. Lett. B542 (2002) 43-48

[2] D.Sarchi et al., Phys. Lett. B601 (2004) 27-33

[3] D.Vretenar et al., Nucl. Phys. A692 (2001) 496-517

[4] S.Goriely, Phys. Lett. B436 (1998) 10-18