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HK: Fachverband Physik der Hadronen und Kerne

HK 54: Hauptvorträge III

HK 54.3: Hauptvortrag

Freitag, 2. März 2018, 12:00–12:30, Audimax

New Phenomena in Gamma-Ray Strength Functions — •Ronald Schwengner — Helmholtz-Zentrum Dresden-Rossendorf

The excitation and deexcitation of atomic nuclei by electromagnetic radiation are fundamental processes in reactions of this many-body quantum system. At high excitation energy and high level density, statistical models are applied to describe reaction rates, which use γ-ray strength functions (γSF) to describe the average transition probabilities in a certain range of excitation energy. The experimental determination and the theoretical understanding of the properties of γSF are important for the accurate description of photonuclear reactions and radiative-capture reactions, which play a central role in the synthesis of the elements in various stellar environments.

We report photon-scattering experiments using bremsstrahlung at the γELBE facility (HZDR) and quasi-monoenergetic, polarized γ beams at the HIγS facility (TUNL, Duke Univ., Durham, USA). Systematic studies of the dipole strength revealed new phenomena that are not described by the analytical approximations currently used in reaction codes. The (γ,γ’) experiments at high energy show considerable contributions to the γSF from the quasicontinuum of states. Combined with (γ,n) cross sections, the (γ,γ’) data provide experimental input γSF for statistical reaction codes.

The experimental studies are complemented by theoretical investigations. Enhancements of γSF at low energy are described on the basis of statistics of transitions from large-scale shell-model calculations.