Seminar: Gamma-ray strength functions at low energy (Ronald Schwengner)

Datum

23.01.2025

Zeit

15:00 - 16:00

Sprache

en

Hauptthema

Willkommen

Andere Themen

Physik, Willkommen

Beschreibung

The excitation and deexcitation of the nucleus by electromagnetic radiation at high excitation energy and high level density are described by means of gamma-ray strength functions (gSF) which represent average transition strengths in a certain energy range. The experimental determination and the theoretical understanding of the properties of gSF has attracted increasing interest because of their importance for the accurate description of photonuclear reactions and the inverse radiative-capture reactions, which play a central role in in the synthesis of the elements in various stellar environments. The standard electric dipole (E1) strength functions used in statistical reaction-model calculations are Lorentz functions adjusted to (gamma,n) reaction data that represent the isovector giant dipole resonance (GDR). To test the low-energy region of gSF below the neutron-separation energy, experiments using photon scattering or light-ion induced reactions are performed, in which nuclear levels below the particle-separation energies are excited. Photon-scattering experiments using broad-band bremsstrahlung at the gELBE facility of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) as well as using quasi-monoenergetic, polarized photon beams produced at the High-Intensity gamma-Ray Source (HIgS), of the Triangle Universities Nuclear Laboratory (TUNL) in Durham, NC, reveal extra E1 strength on top of the tail of a Lorentz function considered as a pygmy dipole resonance (PDR). The analysis including the quasicontinuum in the g-ray spectra and results are presented. Recently, a strong upbend of the gSF toward zero transition energy has been observed in light-ion induced reactions. This low-energy upbend can be described on the basis of large-scale shell-model calculations as caused by a large number of magnetic dipole (M1) transitions linking excited states with configurations dominated by protons and neutrons in high-j orbitals. A study of a series of isotopes from shell closures to open shells is presented that shows a correlation between the low-energy upbend and the scissors mode, a fundamental M1 excitation occurring in deformed nuclei.

Links

• Termindetails auf den Webseiten der TU Dresden (https://tu-dresden.de)

Letztmalig verändert: 23.01.2025, 07:38:33