Electromagnetic excitation of the two-phonon giant dipole resonance

Emling, H.

doi:10.1016/0146-6410(94)90052-3

Cited by 97 publications

(86 citation statements)

References 80 publications

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“…Apparently, the matrix elements for the transition from the GDR (GQR) to the double-GDR (double-GQR) state does not follow the boson-rule [42]. This is borne out by the discrepancy between the experimental cross sections for the excitation of the double-GDR and the double-GQR with the perturbation theory, and with the harmonic oscillator model [7,8,9]. Thus, a Coupled-Channels calculation is useful to determine which matrix elements for the transitions among the giant resonance states reproduce the experimental data.…”

Section: Harmonic Vibrator Modelmentioning

confidence: 87%

“…The double-GDR and double-GQR states do not have exactly twice the energy of the respective GDR and GQR states [7,8,9]. Apparently, the matrix elements for the transition from the GDR (GQR) to the double-GDR (double-GQR) state does not follow the boson-rule [42].…”

Section: Harmonic Vibrator Modelmentioning

confidence: 99%

“…Examples are the studies of multiphonon resonances in the SIS accelerator at the GSI facility, in Darmstadt, Germany [7,8,9]. Important properties of nuclei far from stability [10,11] have also been studied with this method.…”

Section: Introductionmentioning

confidence: 99%

“…a GDR excited on a GDR state) exists then the cross sections for their excitation in heavy ion collisions at relativistic energies are of order of a few hundred of milibarns. These calculations motivated experimentalists at the GSI [7,9] and elsewhere [13,14] to look for the signatures of the DGDR in the laboratory. This has by now become a very active field in nuclear physics with a great theoretical and experimental interest [7,8,9].…”

Section: Introductionmentioning

confidence: 99%

“…[7,9]). A striking feature was observed when either the beam energy was increased, or heavier projectiles were used, or both [12].…”

Section: Introductionmentioning

confidence: 99%

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Microscopic studies of two-phonon giant resonances

Ponomarev

1999

Nuclear Physics A

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A new class of giant resonances in nuclei, namely double giant resonances, is discussed. They are giant resonances built on top of other giant resonances. Investigation on their properties, together with similar studies on low-lying two-phonon states, should give an answer on how far the harmonic picture of boson-type excitations holds in the finite fermion systems like atomic nuclei.The main attention in this review is paid to double giant dipole resonances (DGDR) which are observed in relativistic heavy ion collisions with very large cross sections. A great experimental and theoretical effort is underway to understand the reaction mechanism which leads to the excitation of these states in nuclei, as well as the better microscopic understanding of their properties. The Coulomb mechanism of the excitation of single and double giant resonances in heavy ion collision at different projectile energies is discussed in details. A contribution of the nuclear excitation to the total cross section of the reaction is also considered. The Coulomb excitation of double resonances is described within both, the second-order perturbation theory approach and in coupled-channels calculation. The properties of single and double resonances are considered within the phenomenologic harmonic vibrator model and microscopic quasiparticle-RPA approach. For the last we use the Quasiparticle-Phonon Model (QPM) the basic ideas and formalism of which are presented. The QPM predictions of the DGDR properties (energy centroids, widths, strength distributions, anharmonicities and excitation cross sections) are compared to predictions of harmonic vibrator model, results of other microscopic calculations and experimental data available. : 24.30.Cz, 25.70.De, Pacs

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Section: Harmonic Vibrator Modelmentioning

confidence: 87%

Section: Harmonic Vibrator Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…[7,9]). A striking feature was observed when either the beam energy was increased, or heavier projectiles were used, or both [12].…”

Section: Introductionmentioning

confidence: 99%

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Microscopic studies of two-phonon giant resonances

Ponomarev

1999

Nuclear Physics A

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Multiphonon and “Hot”-Phonon Isovector Electric-Dipole Excitations

et al. 1999

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We argue that a substantial increase in the cross section for Coulomb excitation in the region of the Double Giant Dipole Resonance should be expected from Coulomb excitation of excited states involved in the spreading of the one-phonon resonance, in a manifestation of the Brink-Axel phenomenon. This generates an additional fluctuating amplitude and a corresponding new term to be added incoherently to the usual cross-section. The appropriate extension of an applicable reaction calculation is considered in order to estimate this effect. [4][5][6]. The isoscalar double giant quadrupole resonance has also been observed in the proton emission spectrum from the collision of 40 Ca with 40 Ca at a laboratory energy of 44 A Mev [7].When the data on DGDR excitation for 136 Xe and 197 Au are compared with coupled-channel Coulomb excitation calculations [8], it is found that, in the harmonic approximation, the calculated cross sections are a factor of 2 to 3 smaller than the measured ones. A similar discrepancy, albeit somewhat smaller, is found for 208 Pb.Several effects that are not taken into account in the coupled-channel theory have been considered as possible explanations of this discrepancy. As examples, we mention the effect of anharmonicities [9,10] and the quenching of the 1 + DGDR state [11]. Here we will consider a new potentially important mechanism, which consists in the (one phonon) Coulomb excitation of backgrount states responsible for the large spreading width of the one-phonon GDR, as suggested long ago by Brink and Axel [12]. Due to the complicated background of intrinsic states, the amplitude for this process varies rapidly wth energy and possesses an average close to zero. Its contribution to the cross section can be sizable, however. In close analogy to this situation is the the well-known case of nucleon-nucleus elastic scattering. There, the cross section is the sum of the slowly-varying contribution of average optical scattering and of the fluctuating contribution compound nucleus formation and decay. In figure 1 we show a schematic picture of the couplings involved.We first sumarize our main result. The cross-section for Coulomb excitation to the DGDR energy region contains in fact two distinct components which peak at ∼ 2E GDR . However, while the usual component σ DGDR has a width which may be estimated as ∼ 2Γ GDR , the fluctuating Brink-Axel component has a width which is just ∼ Γ GDR . As a result of this, the bump observed in the two-phonon region has an effective width between these limits. The enhancement factor for the peak-value of the cross-section will be given roughly by (1 + Γ ↓ 1 /Γ 1 ), whereas the crosssection integrated over the peak is just about (1 + 1 2 Γ ↓ 1 /Γ 1 )σ DGDR due to the smaller width of the second component. For heavy nuclei Γ ↓ 1 ∼ Γ 1 , and we get enhancement factors of ∼ 2 and ∼ 3/2 for the peak and for the integrated crosssections respectively. Furthermore, these enhancement factors should be reduced and tend to unity as the collision time becomes shorter t...

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SU(2,1) Model of Multiple Giant Dipole Resonance Coulomb Excitation

2000

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We construct a three-dimensional analytically soluble model of the nonlinear effects in Coulomb excitation of multiphonon giant dipole resonances (GDR) based on the SU(2,1) algebra. The full three-dimensional model predicts enhancement of the double GDR (DGDR) cross sections at high bombarding energies. Enhancement factors for DGDR measured in 13 different processes with various projectiles and targets at different bombarding energies are well reproduced with the same value of the nonlinearity parameter with the exception of the anomalous case of 136 Xe which requires a larger value.

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Electromagnetic excitation of the two-phonon giant dipole resonance

Cited by 97 publications

References 80 publications

Microscopic studies of two-phonon giant resonances

Microscopic studies of two-phonon giant resonances

Multiphonon and “Hot”-Phonon Isovector Electric-Dipole Excitations

SU(2,1) Model of Multiple Giant Dipole Resonance Coulomb Excitation

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