Electroexcitation of 208Pb, distribution of electric dipole and quadrupole strength and fragmentation of the isoscalar quadrupole giant resonance

Kühler, G.; Meuer, Daniel; Müller, Sebastian; Richter, A.; Spamer, E.; Titze, O.; Knüpfer, W.

doi:10.1016/0370-2693(81)90588-8

Cited by 26 publications

(14 citation statements)

References 22 publications

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“…Studies of the low energy spectrum by elastic photon scattering [14], photoneutron [15], and electron scattering [16] have detected fragmented E1 strength in the energy region between 9 and 11 MeV. The fine structure exhausts between 3 and 6% of the E1 sum rule.…”

Section: Introductionmentioning

confidence: 99%

Collectivity of the low-lying dipole strength in relativistic random phase approximation

et al. 2001

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The relativistic random phase approximation is applied in the analysis of the evolution of the isovector dipole response in nuclei with a large neutron excess. The self-consistent framework of relativistic mean-field theory, which has been very successfully applied in the description of ground-state properties of nuclei far from the valley of β-stability, is extended to study the possible onset of low-energy collective isovector dipole modes in nuclei with extreme isospin values.

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Section: Introductionmentioning

confidence: 99%

Collectivity of the low-lying dipole strength in relativistic random phase approximation

et al. 2001

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“…There is also experimental evidence for possible pygmy dipole states in 208 Pb. Studies of the low energy spectrum by elastic photon scattering [11], photoneutron [12], and electron scattering [13] have detected fragmented E1 strength in the energy region between 9 and 11 MeV. The fine structure exhausts between 3 and 6% of the E1 sum rule.…”

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confidence: 99%

Pygmy dipole resonances in the relativistic random phase approximation

et al. 2001

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The isovector dipole response in 208 Pb is described in the framework of a fully self-consistent relativistic random phase approximation. The NL3 parameter set for the effective mean-field Lagrangian with nonlinear meson self-interaction terms, used in the present calculations, reproduces ground state properties as well as the excitation energies of giant resonances in nuclei. In addition to the isovector dipole resonance in 208 Pb, the present analysis predicts the occurrence of low-lying E1 peaks in the energy region between 7 and 11 MeV. In particular, a collective state has been identified whose dynamics correspond to that of a dipole pygmy resonance: the vibration of the excess neutrons against the inert core composed of equal number of protons and neutrons. 1The multipole response of nuclei with large neutron excess has been the subject of many theoretical studies in recent years. Exotic nuclei with extreme neutron to proton ratio exhibit many interesting and unique structure phenomena. In addition to exotic ground state properties, the onset of lowenergy collective isovector modes has been predicted and experimental evidence for these modes in light nuclei has been reported [1]. Catara et al. have studied the low-lying components in strength distributions of weakly bound neutron-rich nuclei [2], and the effect of large neutron excess on the dipole response in the region of the giant dipole resonance in O and Ca isotopes [3]. They have shown that the neutron excess increases the fragmentation of the isovector giant dipole resonance (GDR) and that the radial separation of proton and neutron densities leads to non-vanishing isoscalar transition densities to the GDR states. The fragmentation of the isoscalar and isovector monopole strength in neutron rich Ca isotopes has been studied in Ref. [4], and in Ref.[5] the onset of pygmy dipole resonances in Ca isotopes has been analyzed.The pygmy dipole resonance, which is also the subject of the present study, results from the excess neutrons oscillating out of phase with a core composed of equal number of protons and neutrons. A number of theoretical models have been applied in studies of the dynamics of pygmy dipole resonances. These include: the three-fluid hydrodynamical model (the protons, the neutrons of the same orbitals as protons, and the excess neutrons) [6], the two-fluid (the core fluid and the neutron excess fluid) Steinwedel-Jensen hydrodynamical model [7], density functional theory [5], and the Hartree-Fock plus random phase approximation (RPA) with Skyrme forces [3,8]. More recently, large scale shell model calculations have been performed in studies of pygmy and dipole states in O isotopes [9], and dipole and spin-dipole strength distributions in 11 Li [10]. There is also experimental evidence for possible pygmy dipole states in 208 Pb. Studies of the low energy spectrum by elastic photon scattering [11], photoneutron [12], and electron scattering [13] have detected fragmented E1 strength in the energy region between 9 and 11 MeV. The fine...

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“…The experiments were carried out with a 200 MeV proton beam produced by the Separated Sector Cyclotron (SSC) at iThemba LABS. The protons were scattered inelastically off targets within a wide mass-range, namely 27 Al, 40 Ca, 56 Fe, 58 Ni and 208 Pb. Highly enriched (> 95%) targets with typical areal densities of 1 − 3 mg/cm 2 were used.…”

Section: Methodsmentioning

confidence: 99%

“…Here, the parameters were determined by a least-squares fit to a set of known transitions in 12 C and 27 Al. For further details see ref.…”

Section: Countsmentioning

confidence: 99%

“…Another interesting phenomenon that can be studied in such experiments is that of fine structure in the excitation region of the IVGDR. Pioneering work on the fine structure of giant resonances was reported a long time ago in high energy-resolution (∆E 50 keV) electron scattering experiments at the DALINAC [26,27], where the Isoscalar Giant Quadrupole Resonance (ISGQR) in 208 Pb was investigated. The same structures later seen in high resolution proton scattering experiments [28] and a survey over a wide nuclear mass-range demonstrated that the fine structure is not specific to 208 Pb but generally appears in even-even nuclei [29,30].…”

Section: Introductionmentioning

confidence: 99%

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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$^\circ$

Jingo,

Buthelezi,

Carter

et al. 2018

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A survey of the fine structure of the Isovector Giant Dipole Resonance (IVGDR) was performed, using the recently commissioned Zero-degree Facility of the K600 magnetic spectrometer at iThemba LABS. Inelastic proton scattering at an incident energy of 200 MeV was measured on 27 Al, 40 Ca, 56 Fe, 58 Ni and 208 Pb. A high energy-resolution (∆E 40 keV FWHM) could be achieved after utilising faint-beam and dispersion-matching techniques. Considerable fine structure is observed in the energy region of the IVGDR and characteristic energy scales are extracted from the experimental data by means of a wavelet analysis. The comparison with Quasiparticle-Phonon Model (QPM) calculations provides insight into the relevance of different giant resonance decay mechanisms. Photoabsorption cross sections derived from the data assuming dominance of relativistic Coulomb excitation are in fair agreement with previous work using real photons.

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Electroexcitation of 208Pb, distribution of electric dipole and quadrupole strength and fragmentation of the isoscalar quadrupole giant resonance

Cited by 26 publications

References 22 publications

Collectivity of the low-lying dipole strength in relativistic random phase approximation

Collectivity of the low-lying dipole strength in relativistic random phase approximation

Pygmy dipole resonances in the relativistic random phase approximation

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$^\circ$

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