A recent theoretical prediction of a breaking of axial symmetry in quasi all
heavy nuclei is confronted to a new critical analysis of photon strength
functions of nuclei in the valley of stability. For the photon strength in the
isovector giant dipole resonance (IVGDR) regime a parameterization of GDR
shapes by the sum of three Lorentzians (TLO) is extrapolated to energies below
and above the IVGDR. The impact of non-GDR modes adding to the low energy slope
of photon strength is discussed including recent data on photon scattering and
other radiative processes. These are shown to be concentrated in energy regions
where various model calculations predict intermediate collective strength; thus
they are obviously separate from the IVGDR tail. The triple Lorentzian (TLO)
ansatz for giant dipole resonances is normalized in accordance to the dipole
sum rule. The nuclear droplet model with surface dissipation accounts well for
positions and widths without local, nuclide specific, parameters. Very few and
only global parameters are needed when a breaking of axial symmetry already in
the valley of stability is admitted and hence a reliable prediction for
electric dipole strength functions also outside of it is expected.Comment: 21 pages, 21 figures, PACS: 26.50.+x, 25.20.Dc,27.60.+j Accepted by
Europ. Phys. Journal
