Two-phonon Giant Resonance Research Articles

Anharmonicity of giant resonances

Using the particle-vibration coupling for particles moving in the harmonic oscillator potential, the anharmonicity in two-phonon states of monopole, dipole, and quadrupole giant resonances of shape vibrations is studied. The anharmonic term in both the energy and strength of two-phonon giant resonances vanishes in the leading order of ${N}_{F}\ensuremath{\gg}1.$ Thus, instead of ${A}^{\ensuremath{-}1},$ the calculated energy shift becomes the order of ${A}^{\ensuremath{-}4/3},$ which is still the order of ${A}^{1/3}$ larger than that obtained from a macroscopic description of the vibrations.

Impact-parameter dependence of giant resonance excitations in relativistic heavy-ion collisions

Angular distributions of Xe fragments produced in peripheral collisions of a 136 Xe beam ~700 MeV/nucleon! with 208 Pb and nat Sn targets were measured. Equivalent sharp-cutoff minimum impact parameters were derived on the basis of a semiclassical description for the electromagnetic excitation of one- and two-phonon giant resonances. The results are compared with current standard parametrizations of minimum impact parameters and with the soft-spheres model using realistic mass density distributions for projectile and targets. @S0556-2813~99!50611-0#

Microscopic studies of two-phonon giant resonances

Position, width and excitation probability in relativistic heavy ion collisions of two-phonon giant dipole resonances in spherical and deformed nuclei are considered.

Double giant resonances in deformed nuclei

We report on the first microscopic study of the properties of two-phonon giant resonances in deformed nuclei. The cross sections of the excitation of the giant dipole and the double giant dipole resonances in relativistic heavy ion collisions are calculated. We predict that the double giant dipole resonance has a one-bump structure with a centroid 0.8 MeV higher than twice the energy for the single giant dipole resonance in the reaction under consideration. The width of the double resonance equals 1.33 of that for the single resonance.

Multiphonon giant resonances: Experimental status and perspectives

Recently, decisive progress has been made in the search for multiphonon states built with giant resonances. This paper will first focus on the different probes used to excite multiphonon states, and the experimental methods used to characterize these states. Several examples of experiments where the two-phonon giant resonance has been observed are described. The possibility of signing two-phonon strength through its direct decay by particle emission is then discussed in detail, and the results of the ongoing experimental program at GANIL are presented. Finally, the potential of different methods for the future observation of three-phonon states is briefly examined.

Giant resonances and intermediate energy heavy ions: Electromagnetic decay experiments

We briefly explore how large cross sections for excitation of both isoscalar and isovector giant multipole resonances which can be obtained using intermediate energy heavy-ion reactions can be utilized in photon-decay coincidence experiments to provide new information on subjects ranging from basic nuclear structure properties to resonance damping and pre-compound decay. We also discuss experiments in which photon-decay techniques are used as a tag to isolate and identify very weakly excited modes, enabling us to explore such diverse subjects as hadronic excitation of the giant dipole resonance, the distribution of isovector quadrupole strength in 208Pb, and the excitation of two-phonon giant resonance strength.