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 2_ms⁺ 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. Yates⁴ — ¹Institut 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 1_ms⁺ state the 2_ms⁺ state is of great interest [3,4,5]. The identification of the 2_ms⁺ 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 2_ms⁺ state has been identified previously in the nuclei ¹⁴²Ce [4] and ¹³⁴Ba [5] from lifetime measurements using Coulomb excitation and (n,n^′γ) reactions, respectively.

For a more detailed investigation of the 2_ms⁺ state in nuclei of the mass region A=100–150 we performed several experiments with different probes. Results on the 2_ms⁺ 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.