Instantaneous Shape Sampling - a model for the $\gamma$-absorption cross section of transitional nuclei

Abstract

The influence of the quadrupole shape fluctuations on the dipole vibrations in transitional nuclei is investigated in the framework of the Instantaneous Shape Sampling Model, which combines the Interacting Boson Model for the slow collective quadrupole motion with the Random Phase Approximation for the rapid dipole vibrations. Coupling to the complex background configurations is taken into account by folding the results with a Lorentzian with an energy dependent width. The low-energy energy portion of the $\gamma$- absorption cross section, which is important for photo-nuclear processes, is studied for the isotopic series of Kr, Xe, Ba, and Sm. The experimental cross sections are well reproduced. The low-energy cross section is determined by the Landau fragmentation of the dipole strength and its redistribution caused by the shape fluctuations. Collisional damping only wipes out fluctuations of the absorption cross section, generating the smooth energy dependence observed in experiment. In the case of semi-magic nuclei, shallow pygmy resonances are found in agreement with experiment.

References in corpus (12)

• Exotic modes of excitation in atomic nuclei far from stability
• Investigation of Pygmy Dipole Resonances in the Tin Region
• Relativistic quasiparticle time blocking approximation. Dipole response of open-shell nuclei
• Pygmy dipole strength in 90Zr
• Particle-vibration coupling within covariant density functional theory
• Low-lying dipole response in the Relativistic Quasiparticle Time Blocking Approximation and its influence on neutron capture cross sections
• Photon data shed new light upon the GDR spreading width in heavy nuclei
• Relativistic quasiparticle time blocking approximation. II. Pygmy dipole resonance in neutron-rich nuclei
• Skyrme-Rpa Description of Dipole Giant Resonance in Heavy and Superheavy Nuclei
• Self-Consistent Separable Rpa for Skyrme Forces: Giant Resonances in Axial Nuclei
• Electromagnetic Dipole Strength in Transitional Nuclei
• Low-energy Dipole Excitations in Nuclei at the N=50,82 and Z=50 Shell Closures as Signatures for a Neutron Skin