Two-phonon giant dipole resonance in 208Pb

Boretzky, K.; Stroth, J.; Wajda, E.; Aumann, T.; Blaich, Th.; Cub, J.; Elze, Th. W.; Emling, H.; Henning, W.; Holzmann, R.; Klingler, H.; Kulessa, R.; Kratz, J. V.; Lambrecht, Daniel S.; Leifels, Y.; Lubkiewicz, E.; Stelzer, K.; Waluś, W.; Zinser, M.; Zude, E.

doi:10.1016/0370-2693(96)00797-6

Cited by 61 publications

(81 citation statements)

References 20 publications

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“…The calculated cross section in coupled-channels for both GDR and DGDR are somewhat smaller than reported in experimental findings [54,105]. This is not surprising since as mentioned above our chosen six 1 − states exhaust only 90.6% of EWSR while the photo-neutron data [32] indicate that this value equals to 122%.…”

Section: + Component Of the Dgdrmentioning

confidence: 45%

Section: + Component Of the Dgdrmentioning

confidence: 87%

“…The experimental findings [54] yield the value R exp = 0.116±0.014. The reported [54] disagreement R exp /R calc =1.33±0.16 is the result of a comparison with R calc obtained within a folding model, assuming 122% of the EWSR. We get a somewhat larger value of R calc (taking into account our scaling procedure) because the B(E1) strength distribution over our six 1 − states is not symmetrical with respect to the centroid energy, E GDR : the lower part is enhanced.…”

Section: + Component Of the Dgdrmentioning

confidence: 87%

“…Let us consider the excitation of the DGDR in the projectile for a 208 Pb (640A MeV) + 208 Pb collision, according to the experiment in Ref. [54], and use the minimum value of the impact parameter, b= 15.54 fm, corresponding to the parameterization of Ref. [43].…”

Section: + Component Of the Dgdrmentioning

confidence: 99%

“…38 shows that the direct excitation of two-phonon 1 − states cannot be completely excluded from consideration of this reaction. Integrated over the energy interval from 20 to 35 MeV these states give a cross section of 50.3 mb which should be compared to the experimental cross section in the DGDR region for the 208 Pb (640A MeV) + 208 Pb reaction which is equal to 380 mb [54].…”

Section: + Component Of the Dgdrmentioning

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: + Component Of the Dgdrmentioning

confidence: 45%

Section: + Component Of the Dgdrmentioning

confidence: 87%

Section: + Component Of the Dgdrmentioning

confidence: 87%

Section: + Component Of the Dgdrmentioning

confidence: 99%

Section: + Component Of the Dgdrmentioning

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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The nuclear collective motion

Nazarewicz

2001

An Advanced Course in Modern Nuclear Physics

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Abstract. Current d e v elopments in nuclear structure are discussed from a theoretical perspective. First, the progress in theoretical modeling of nuclei is reviewed. This is followed by the discussion of nuclear time scales, nuclear collective modes, and nuclear deformations. Some perspectives on nuclear structure research far from stability a r e given. Finally, i n terdisciplinary aspects of the nuclear many-body problem are outlined.

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Two-phonon giant dipole resonance in 208Pb

Cited by 61 publications

References 20 publications

Microscopic studies of two-phonon giant resonances

Microscopic studies of two-phonon giant resonances

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

The nuclear collective motion

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