Bochum 1998 – scientific programme

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HK: Hadronen und Kerne

HK 28: Spectroscopy: 70 ≤ A < 110

HK 28.3: Group Report

Tuesday, March 17, 1998, 14:30–15:00, D

Magnetic dipole bands in ⁸²Rb, ⁸³Rb and ⁸⁴Rb ^⋆ — •R. Schwengner¹, H. Schnare¹, S. Frauendorf¹, L. Käubler¹, F. Dönau¹, H. Prade¹, E. Grosse¹, A. Jungclaus², K.P. Lieb², Ch. Lingk², S. Skoda³, J. Eberth³, G. de Angelis⁴, A. Gadea⁴, E. Farnea⁴, C.A. Ur⁴, and G. Lo Bianco⁵ — ¹Institut für Kern- und Hadronenphysik, FZ Rossendorf, D-01314 Dresden — ²II. Physikalisches Institut, Universität Göttingen, D-37073 Göttingen — ³Institut für Kernphysik, Universität zu Köln, D-50937 Köln — ⁴Laboratori Nazionali INFN, I-35020 Legnaro — ⁵INFN - Sezione di Milano, I-20133 Milano

Magnetic rotation is predicted in several mass regions including a certain region around A = 80 [1] where the deformation is small and the particle-like protons fill the (fp) shell while there are only few g_9/2 neutron holes in the N = 50 shell. Our investigation of a dipole band in the N = 44 nucleus ⁷⁹Br has shown that this band includes a strong magnetic component but also collective rotation [2].

To continue the search for magnetic rotation in this mass region we studied the isotopes ⁸²Rb₄₅, ⁸³Rb₄₆ and ⁸⁴Rb₄₇. Excited states in these nuclei were populated via the reaction ¹¹B + ⁷⁶Ge at E = 50 MeV using the ¹¹B beam of the XTU tandem accelerator of the LNL Legnaro. Gamma rays were detected with the spectrometer GASP. A total of 1 × 10⁸ three-fold coincidence events was recorded.

Regular dipole bands without signature splitting have been identified in the odd-odd nuclei ⁸²Rb and ⁸⁴Rb. They comprise B(M1)/B(E2) ratios of up to 20 µ_N² / e²b², decreasing with increasing spin. These bands may represent magnetic rotation observed for the first time in odd-odd nuclei in this mass region. In contrast, the dipole sequences found in the odd-even nucleus ⁸³Rb are not regular and display signature splitting. Possible configurations of the dipole bands are discussed in terms of the tilted-axis cranking model.

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[1] S. Frauendorf, Z. Phys. A 358 (1997) 163.

[2] T. Servene et al., Annual report 1996, FZR-179 (1997) 69.

^⋆ Supported by the BMBF.