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Bochum 1998 – wissenschaftliches Programm

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HK: Hadronen und Kerne

HK 50: Spectroscopy: 130 ≤ A ≤ 180

HK 50.1: Gruppenbericht

Mittwoch, 18. März 1998, 14:00–14:30, D

Investigation of the 2ms+ mixed symmetry state with different probes — •N. Pietralla1, I. Wiedenhöver2, T. Klug1, D. Belic3, P. von Brentano1, T. Eckert3, C. Fransen1, A. Gade1, A. Gelberg1, R.-D. Herzberg1, U. Kneissl3, H. Maser3, A. Nord3, H.H. Pitz3, V. Werner1, and S. Yates41Institut für Kernphysik, Universität zu Köln — 2Argonne National Laboratory, Argonne, IL, USA — 3Institut für Strahlenphysik, Universität Stuttgart — 4Department of Chemistry, University of Kentucky, Lexington, KE, USA

In the excitation spectra predicted by the proton-neutron version of the Interacting Boson Model (IBM-2) exist multiple isoscalar and isovector quadrupole excitations of the ground state. Around 2 – 3 MeV this model predicts the existence of so-called mixed-symmetry states [1]. The best known example of such kind of excitations is the 1+ scissors mode which has been discovered by Richter and coworkers [2]. Besides the 1ms+ state the 2ms+ state is of great interest [3,4,5]. The identification of the 2ms+ state requires, in addition to dominant M1 decay branches [3], the knowledge of the lifetime in order to judge the collectivity of this excitation. The 2ms+ state has been identified previously in the nuclei 142Ce [4] and 134Ba [5] from lifetime measurements using Coulomb excitation and (n,nγ) reactions, respectively.

For a more detailed investigation of the 2ms+ state in nuclei of the mass region A=100–150 we performed several experiments with different probes. Results on the 2ms+ state which we obtained in the reactions 136Ba(γ,γ), 125Te(α,n)128Xe [6], 132Pr(β+)132Ce, and 144Nd(γ,γ) [7] will be reported. These experiments have been performed at the photon scattering facility of the Stuttgart Dynamitron accelerator and at the Cologne Tandem accelerator. A comparison to IBM-2 calculations will be given.
Supported by the Deutsche Forschungsgemeinschaft, Project Nos. Br 799/6-2/8-1 and Kn 154-30.
[1] F. Iachello, Phys. Rev. Lett. 53, (1984) 1427.
[2] D. Bohle, A. Richter et al., Phys. Lett. B 137, (1984) 27.
[3] W.D. Hamilton et al., Phys. Rev. Lett. 53, (1984) 2469.
[4] W.J. Vermeer et al., Phys. Rev. C 38, (1988) R2983.
[5] G. Molnár et al., Phys. Rev. C 37, (1988) 898.
[6] I. Wiedenhöver et al., Phys. Rev. C 56, (1997) R, in press.
[7] T. Eckert et al., Phys. Rev. C 56, (1997) 1256.

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