Berlin 2005 – wissenschaftliches Programm
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HK: Physik der Hadronen und Kerne
HK 3: Kernphysik/Spektroskopie
HK 3.1: Gruppenbericht
Freitag, 4. März 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