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HK: Fachverband Physik der Hadronen und Kerne

HK 56: Struktur und Dynamik von Kernen IX

HK 56.8: Vortrag

Donnerstag, 18. März 2010, 18:45–19:00, HG VII

Enhancement of dipole strength below the neutron-separation energy in ¹³⁹La — A. Makinaga¹, G. Rusev^2,3, •R. Schwengner², F. Doenau², D. Bemmerer², R. Beyer², P. Crespo^2,4, M. Erhard^2,5, A.R. Junghans², J. Klug^2,6, K. Kosev², C. Nair^2,7, K.D. Schilling², and A. Wagner² — ¹Hokkaido University, Sapporo, 060-0810, Japan — ²Forschungszentrum Dresden-Rossendorf, 01314 Dresden, Germany — ³Duke University and TUNL, Durham, NC 27708, USA — ⁴University of Coimbra, 3004-516 Coimbra, Portugal — ⁵INFN, Sezione di Padova, 35131 Padova, Italy — ⁶Vattenfall Power Consultant, 16216 Stockholm, Sweden — ⁷Argonne National Laboratory, Argonne, IL 60439, USA

The photoabsorption cross section of ¹³⁹La was measured up to the neutron-separation energy using bremsstrahlung produced at the electron accelerator ELBE of the Forschungszentrum Dresden-Rossendorf with a beam of 11.5 MeV kinetic energy. To estimate branching ratios of transitions from states in the quasicontinuum, we performed simulations of γ-ray cascades. The photoabsorption cross section deduced from the resulting intensities of the ground-state transitions can be combined with photoneutron cross sections to obtain data in a wide energy range up to the giant dipole resonance (GDR). We observe an enhancement of electric dipole strength relative to a Lorentz-like tail of the GDR that cannot be quantitatively reproduced by current model calculations.