Bochum 1998 – scientific programme
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HK: Hadronen und Kerne
HK 17: Giant Resonances
HK 17.2: Group Report
Monday, March 16, 1998, 17:30–18:00, E
Magnetic quadrupole resonances in 48Ca and 90Zr from 180∘ electron scattering⋆ — •B. Reitz, S. Diederich, F. Hofmann, A. Mai, P. von Neumann-Cosel, F. Neumeyer, A. Richter, G. Schrieder, and J. Wambach — Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany
The nuclei 48Ca and 90Zr were investigated in electron scattering under 180∘. The measured momentum transfer range q ≃ 0.35 − 0.8 fm−1 provides an enhanced selectivity to the low-multipolarity nuclear magnetic response. The complete M2 strength could be extracted in both nuclei up to about 15 MeV by combination of a form factor analysis for resolved transitions plus a fluctuation analysis for unresolved parts in the background. Furthermore, a multipole decomposition provides new insight into an old discrepancy between electron and hadron scattering about the strength of the spin magnetic dipole resonance in 90Zr.
The resulting strength distributions are compared to SRPA calculations which provide, for the first time, a rather accurate description of the strong spreading and fragmentation of the M2 resonance. >From the comparison to theory the quenching factor of the spin M2 strength can be extracted. One finds reduction values reasonably close to the factor of about 0.5 established for M1 quenching in heavy nuclei. The experimental results are discusssed with respect to non-energy-weighted and energy-weighted sum rules for the M2 strength.
⋆ Supported by the DFG under contract Ri 242/12-1.