Fine structure of the isovector giant dipole resonance in Pb 208: Characteristic scales and level densities

states is related to local fluctuations of the cross sections in the energy region of the IVGDR, where contributions from states with other spin parities can be neglected. The magnitude of the fluctuations is determined by the autocorrelation function. Results: Scales in the fine structure of the IVGDR in 208 Pb are found at 80, 130, 220, 430, 640, and 960 keV, and at 1.75 MeV. The values of the most prominent scales can be reasonably well reproduced by the microscopic calculations although they generally yield a smaller number of scales. The inclusion of complex configurations in the calculations changes the E1 strength distributions but the impact on the wavelet power spectra and characteristic scales is limited. The level density of 1 − states is extracted in the excitation energy range 9‐12.5 MeV and compared to a variety of phenomenological and microscopic models. Conclusions: In both models the major scales are already present at the one-particle one-hole level indicating Landau damping as a dominant mechanism responsible for the fine structure of the IVGDR in contrast to the isoscalargiantquadrupoleresonance,wherefinestructurearisesfromthecouplingtolow-lyingsurfacevibrations. The back-shifted Fermi gas model parametrization of Rauscher et al., Phys. Rev. C 56, 1613 (1997) describes the level-density data well, while other phenomenological and microscopic approaches fail to reproduce absolute values or the energy dependence or both.