Effect of broken axial symmetry on the electric dipole strength and the collective enhancement of level densities in heavy nuclei

Abstract

The basic parameters for calculations of radiative neutron capture , photon strength functions and nuclear level densities near the neutron separation energy are determined based on experimental data without an ad-hoc assumption about axial symmetry - at variance to previous analysis. Surprisingly few global fit parameters are needed in addition to information on nuclear deformation, taken from Hartree Fock Bogolyubov (HFB) calculations with the Gogny force, and the generator coordinator method (GCM) assures properly defined angular momentum. For a large number of nuclei the GDR shapes and the photon strength are described by the sum of three Lorentzians (TLO), extrapolated to low energies and normalized in accordance to the dipole sum rule. Level densities are influenced strongly by the significant collective enhancement based on the breaking of shape symmetry. The replacement of axial symmetry by the less stringent requirement of invariance against rotation by 180 degree leads to a novel prediction for radiative neutron capture. It compares well to recent compilations of average radiative widths and Maxwellian average cross sections for neutron capture by even target nuclei. An extension to higher spin promises a reliable prediction for various compound nuclear reactions also outside the valley of stability. Such predictions are of high importance for future nuclear energy systems and waste transmutation as well as for the understanding of the cosmic synthesis of heavy elements.

Pacs. Nos.:21.10.Ma, 24.30.Cz, 24.60.Dr, 25.20.Dc, 25.40.Lw, 26.20.Kn; 25 pages, 12 figures; to appear in Physica Scripta, special issue on "Shapes and symmetries in Nuclei" (2017)

References in corpus (7)

• Impact of a low-energy enhancement in the gamma-ray strength function on the radiative neutron-capture
• Photon data shed new light upon the GDR spreading width in heavy nuclei
• Systematics of the first 2+ excitation with the Gogny interaction
• Experimental study of the electric dipole strength in the even Mo nuclei and its deformation dependence
• Photoactivation experiment on 197Au and its implications for the dipole strength in heavy nuclei
• Electromagnetic Dipole Strength in Transitional Nuclei
• Broken axial symmetry as essential feature to predict radiative capture in heavy nuclei

Cited by in corpus (2)

• Gamma decay of the ${}^{154}$Sm Isovector Giant Dipole Resonance: Smekal-Raman Scattering as a Novel Probe of Nuclear Ground-State Deformation
• Broken axial symmetry as essential feature for a consistent modelling of various observables in heavy nuclei