  The IVGDR in 208Pb has been measured with high energy resolution with the
(p,p') reaction under extreme forward angles and shows considerable fine
structure. Characteristic scales are extracted from the spectra with a wavelet
analysis based on continuous wavelet transforms. Comparison with corresponding
analyses of B(E1) strength distributions from microscopic model calculations in
the framework of the QPM and relativistic RPA allow to identify giant resonance
decay mechanisms responsible for the fine structure. The level density of 1-
states can be related to local fluctuations of the cross sections in the energy
region of the IVGDR. The magnitude of the fluctuations is determined by the
autocorrelation function. Scales in the fine structure of the IVGDR in 208Pb
are found at 80, 130, 220, 430, 640, 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. 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 isoscalar giant quadrupole resonance,
where fine structure arises from the coupling to low-lying surface vibrations.
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. The back-shifted Fermi gas model
parameterization of Rauscher et al., Phys. Rev. C 56, 1613 (1997) describes the
level-density data well, while other phenomeological and microscopic approaches
fail to reproduce absolute values or the energy dependence or both.
