Darmstadt 2008 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 8: Kernphysik / Spektroskopie

HK 8.3: Talk

Monday, March 10, 2008, 14:30–14:45, 2G

Dipole strength in ⁸⁹Y and ⁹⁰Zr up to the neutron-separation energy ^* — •R. Schwengner¹, G. Rusev^1,2, N. Tsoneva³, N. Benouaret^1,4, R. Beyer¹, F. Doenau¹, M. Erhard¹, E. Grosse^1,5, A.R. Junghans¹, J. Klug¹, K. Kosev¹, C. Nair¹, K.D. Schilling¹, and A. Wagner¹ — ¹Forschungszentrum Dresden-Rossendorf, 01314 Dresden — ²Duke University, Durham, NC 27708, USA — ³Universität Gießen, 35392 Gießen — ⁴Université d’Alger, 16111 Alger, Algerie — ⁵Technische Universität Dresden, 01062 Dresden

Dipole and quadrupole excitations in the semimagic N=50 nuclei ⁸⁹Y and ⁹⁰Zr were investigated at the superconducting electron linear accelerator ELBE with bremsstrahlung produced at electron energies from 9 to 13 MeV. About 200 γ transitions in ⁸⁹Y and 180 in ⁹⁰Zr were identified up to about 11 and 12 MeV, respectively.

Statistical methods were applied to estimate the contributions of inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. The photoabsorption cross sections obtained in this way provide information about the dipole-strength function on the tail of the giant dipole resonance (GDR) towards energies below the neutron-separation energy. We observed extra dipole strength with respect to a smooth extrapolation of the GDR in the energy range from about 6 – 11 MeV.

The observed extra strength is compared with results of calculations within the Quasiparticle-Phonon Model, which also make predictions about the nature of the strength.

^* Supported by the DFG.