Bochum 1998 – wissenschaftliches Programm

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HK: Hadronen und Kerne

HK 7: Nuclear Moments

HK 7.3: Vortrag

Montag, 16. März 1998, 14:30–14:45, E

Measurement of the electric quadrupole moments of ²⁶⁻³¹Na — •S. Wilbert¹, W. Geithner¹, U. Georg¹, S. Kappertz¹, M. Keim², P. Lievens³, R. Neugart¹, L. Vermeeren³, B.A. Brown⁴, and ISOLDE Collaboration² — ¹Inst. für Physik, Universität Mainz — ²CERN, Geneva — ³Dept. Natuurkunde, K.U. Leuven — ⁴Michigan State Univ., East Lansing, USA

The neutron-rich sodium isotopes close to the N shell closure exhibit strong deviations from pure sd-configurations which can be understood as deformation effects. We have investigated the quadrupole moments of ²⁶⁻³¹Na using β-NMR techniques. The beams of short-lived isotopes obtained from ISOLDE are spin-polarized by optical pumping. The atoms are implanted into single crystals of non-cubic symmetry (LiNbO₃, Mg, NaNO₃). The interaction between the nuclear quadrupole moment and the internal field gradient of the lattice leads to a 2I-fold splitting of the NMR signal. In the last year the measurements at the N shell closure were completed, and the quadrupole moments were determined for the full series of isotopes, ²⁶⁻³¹Na. >From a measurement on ²⁸Na in NaNO₃ for which the gradient at the substitutional sodium site is known from classical NMR, a calibration of the field gradients was obtained. These results are discussed in comparison with recent shell-model calculations including fp-shell admixtures. In this context the sign of the quadrupole moments, determined from the relative line intensities, is important.