Description of dipole strength in heavy nuclei in conformity with their quadrupole degrees of freedom

E Grosse,R Massarczyk,A.R Junghans,G Schramm,R Schwengner

doi:10.1051/epjconf/20122104003

E Grosse, R Massarczyk + Show 3 more

Open Access

https://doi.org/10.1051/epjconf/20122104003

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Abstract

In conformity to new findings about the widespread occurrence of triaxiality arguments are given in favor of a description of the giant dipole resonance in heavy nuclei by the sum of three Lorentzians. This TLO parameterization allows a strict use of resonance widths {\Gamma} in accordance to the theoretically founded power law relation to the resonance energy. No additional variation of {\Gamma} with the photon energy and no violation of the sum rule are necessary to obtain a good agreement to nuclear photo-effect, photon scattering and radiative capture data. Photon strength other than E1 has a small effect, but the influence of the level density on photon emission probabilities needs further investigation.

Highlights

In conformity to new findings about the widespread occurrence of triaxiality arguments are given in favor of a description of the giant dipole resonance in heavy nuclei by the sum of three Lorentzians
The practice of extracting the isovector giant dipole resonance (IVGDR) width from a fit to the photon absorption data for individual nuclei is at clear variance to the combination of the predictions for Eo and Γ, both based on hydro-dynamical considerations widely accepted for the description of the IVGDR
The energy integrated electric dipole strength of nuclei is strongly dominated by the IVGDR such that a deviation there results in a corresponding change in the dipole sum

Summary

Deformation and triaxiality of nuclear shapes

As seen from the different apparent widths of the IVGDR-distributions in the five isotopes of Mo, their different ground state deformation has a considerable influence. The right part of the Figure is taken from a single Lorentzian fit to the IVGDR peak area as published previously [49], which apparently overestimates the width Γ This had suggested the inclusion of an explicit photon energy dependence [49-51] which, if perpetuated to higher energy, would enhance the integral by up to 80 % above the TRK sum. The introduction of triaxiality as proposed here (TLO) achieves good agreement with smaller Γ in agreement to the power law As this has an appreciable influence on the energy range with high sensitivity to gamma decay (cf left panel of Figure 8) it is of interest to regard compound nucleus reactions with photons in the exit channel

Photon strength and radiative capture

Findings

Conclusions