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HK: Hadronen und Kerne

HK 7: Nuclear Moments

HK 7.1: Vortrag

Montag, 16. März 1998, 14:00–14:15, E

Measurement of the magnetic moment of ¹¹Be — •S. Kappertz¹, M. Keim², S. Wilbert², W. Geithner¹, R. Neugart¹, P. Lievens³, L. Vermeeren³, and ISOLDE Collaboration² — ¹Inst. für Physik, Univ. Mainz — ²CERN, Geneva — ³Dept. Natuurkunde, K.U. Leuven

Neutron halo nuclei such as ¹¹Li and ¹¹Be have been investigated mainly in intermediate-energy heavy-ion reactions. We report on a measurement of the magnetic moment of the 1/2⁺ ground state of ¹¹Be. Actual theoretic models result in a magnetic moment depending on the admixture of the |¹⁰Be(2+)× d_5/2;1/2⁺ ⟩ configuration to the (ν1s_1/2) halo orbit. We have investigated the magnetic moment of ¹¹Be using the β-NMR technique on ¹¹Be nuclei implanted in a beryllium single crystal. For preparation, we measured the isotope shift and hyperfine structure splitting of ^7,10Be using collinear laser spectroscopy. The Be isotopes are obtained at ISOLDE from proton-induced fragmentation reactions in a UC₂ target which is connected to a two-step laser ionization source. The ¹¹Be⁺ ion beam is spin-polarized by optical pumping. The ions are implanted into a Be single crystal placed in a static magnetic field of ∼ 0.3 T. Nuclear magnetic resonance destroys the polarization which is detected via the asymmetry of the β-radiation. The relative long half-life of 13.8 s requires cooling to about 50 K in order to preserve the nuclear spin polarization in the crystal lattice. A calibration of the NMR-field is obtained from a reference measurement on ⁸Li. The results are discussed in comparison with recent shell-model calculations.