Gross, intermediate and fine structure of nuclear giant resonances: Evidence for doorway states

Abstract

We review the phenomenon of fine structure of nuclear giant resonances and its relation to different resonance decay mechanisms. Wavelet analysis of the experimental spectra provides quantitative information on the fine structure in terms of characteristic scales. A comparable analysis of resonance strength distributions from microscopic approaches incorporating one or several of the resonance decay mechanisms allows conclusions on the source of the fine structure. For the isoscalar giant quadrupole resonance (ISGQR), spreading through the first step of the doorway mechanism, i.e.\ coupling between one particle-one hole ($1p1h$) and two particle-two hole ($2p2h$) states is identified as the relevant mechanism. In heavy nuclei it is dominated by coupling to low-lying surface vibrations, while in lighter nuclei stochastic coupling becomes increasingly important. The fine structure observed for the isovector giant dipole resonance (IVGDR) arises mainly from the fragmentation of the $1p1h$ strength (Landau damping), although some indications for the relevance of the spreading width are also found.

arXiv comment15 pages, 16 figures. Submitted to Eur. Phys. J A, special issue "Giant, pygmy, pairing resonances and related topics"

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• Evolution of the isoscalar giant monopole resonance in the Ca isotope chain
• Damping of the isovector giant dipole resonance in ${}^{40,48}$Ca
• Systematics of the low-energy electric dipole strength in the Sn isotopic chain
• Electric dipole polarizability of ${}^{58}$Ni
• Electric dipole polarizability constraints on neutron skin and symmetry energy
• Angela and the electric dipole response -- giant and pygmy, hot and cold, isoscalar and isovector
• Recent applications of the subtracted second RPA method