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

Abstract

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.

11 pages, 9 figures, Phys. Rev. C (in press)

References in corpus (5)

• Particle-vibration coupling within covariant density functional theory
• Crossover from vibrational to rotational collectivity in heavy nuclei in the shell-model Monte Carlo approach
• Test of nuclear level density inputs for Hauser-Feshbach model calculations
• Fine structure of the isoscalar giant quadrupole resonance in 40Ca due to Landau damping?
• Microscopic calculation of symmetry projected nuclear level densities

Cited by in corpus (33)

• Nuclear Equation of State from ground and collective excited state properties of nuclei
• Low-energy electric dipole response in 120Sn
• Low-energy dipole strength in 112,120Sn
• Electric and magnetic dipole modes in high-resolution inelastic proton scattering at $0^{\circ }$
• Test of the Brink-Axel hypothesis for the pygmy dipole resonance
• Electric and magnetic dipole strength in 112,114,116,118,120,124Sn
• Toward an accurate strongly-coupled many-body theory within the equation of motion framework
• Finite-temperature relativistic nuclear field theory: an application to the dipole response
• Dipole response in 208Pb within a self-consistent multiphonon approach
• Evolution of the dipole polarizability in the stable tin isotope chain
• Temperature dependence of nuclear spin-isospin response and beta decay in hot astrophysical environments
• Benchmarking mean-field approximations to level densities
• Nuclear Dipole Response in the Finite-Temperature Relativistic Time Blocking Approximation
• Gamma strength function and level density of ${}^{208}$Pb from forward-angle proton scattering at 295 MeV
• Fine Structure of the Isovector Giant Dipole Resonance in ${}^{142-150}$Nd and ${}^{152}$Sm
• Many-body correlations in nuclear superfluidity
• Origin of fine structure of the giant dipole resonance in sd-shell nuclei
• Wavelet signatures of $K$-splitting of the Isoscalar Giant Quadrupole Resonance in deformed nuclei from high-resolution (p,p${}^{\prime }$) scattering off ${}^{146,148,150}$Nd
• Nuclear level densities and $\gamma$-ray strength functions in ${}^{120,124}$Sn isotopes: impact of Porter-Thomas fluctuations
• Nuclear response in a finite-temperature relativistic framework
• Microscopic response theory for strongly-coupled superfluid fermionic systems
• Damping of the isovector giant dipole resonance in ${}^{40,48}$Ca
• Studies of the Giant Dipole Resonance in ${}^{27}$Al, ${}^{40}$Ca, ${}^{56}$Fe, ${}^{58}$Ni and ${}^{208}$Pb with high energy-resolution inelastic proton scattering under 0${}^{\circ }$
• Gross, intermediate and fine structure of nuclear giant resonances: Evidence for doorway states
• Electric dipole polarizability of ${}^{58}$Ni
• Learning the structure of giant resonances from their $\gamma$-decay
• Determination of the ${}^{60}$Zn level density from neutron evaporation spectra
• Photoneutron cross section measurements on ${}^{208}$Pb in the Giant Dipole Resonance region
• Angela and the electric dipole response -- giant and pygmy, hot and cold, isoscalar and isovector
• Isospin dynamics in nuclear structure
• Monopole Excitation and Nuclear Compressibility: Present and Future Perspectives
• Recent applications of the subtracted second RPA method
• Nuclear response at zero and finite temperature