Photon scattering from<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">Zr</mml:mi></mml:mrow><mml:mprescripts /><mml:mrow /><mml:mrow><mml:mn>90</mml:mn></mml:mrow><mml:mrow /><mml:mrow /></mml:mmultiscripts></mml:mrow></mml:math>below neutron emission threshold

Alarcón, R.; Laszewski, R. M.; Nathan, A. M.; Hoblit, S.

doi:10.1103/physrevc.36.954

Cited by 23 publications

(40 citation statements)

References 16 publications

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“…The used E1 strength function is taken from the experimental E1 σ γT [13,19]. σ γT was fit with a phenomenological function which reproduced the shape at all energies including the PDRs and the exponential drop at low energy.…”

Section: Fig 2 (Color Online)mentioning

confidence: 99%

“…The BH has been shown to be a reasonable concept for the GDR at low excitation energies in a variety of experiments, including those measuring average intensities of primary transitions from (n,γ) [11], (p,γ) [12], and (γ, γ ′ ) reactions [13]. Reactions with light ions which double excite the GDR also substantiate the BH [14,15].…”

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confidence: 99%

“…This was done by measuring the photoabsorption cross section and ground state branching ratio at several beam energies, and testing their mutual consistency within the nuclear statistical model [13,19]. The 142 Nd(γ,n) cross section was additionally measured to constrain the low-energy tail of the GDR above the neutron separation energy, since the extrapolation of the GDR can affect statistical-model calculations.…”

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confidence: 99%

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Evidence for radiative coupling of the pygmy dipole resonance to excited states

et al. 2012

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Section: Fig 2 (Color Online)mentioning

confidence: 99%

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confidence: 99%

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Evidence for radiative coupling of the pygmy dipole resonance to excited states

et al. 2012

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“…Because in the nuclear realizations the levels were created randomly starting from the ground state instead of starting with the known first excited state at 2.2 MeV, the distribution of the branching transitions continues to the energy bin of the ground-state transitions. These spectra resemble qualitatively the ones measured in an experiment on 90 Zr using tagged photons [4]. Starting from the high-energy end of the experimental spectrum, which contains ground-state transitions only, the simulated intensities of the ground-state transitions were normalized to the experimental ones in the considered bin and the intensity distribution of the branching transitions was subtracted from the experimental spectrum.…”

Section: Determination Of the Dipole-strength Distributionmentioning

confidence: 99%

“…Dipole-strength distributions up to neutron-separation energies have been studied for only few nuclides in experiments with monoenergetic photons (see, e.g., Refs. [1,2,3,4]) and in experiments with bremsstrahlung (see, e.g., Ref. [5] and Refs.…”

Section: Introductionmentioning

confidence: 99%

Pygmy dipole strength inZr90

et al. 2008

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The dipole response of the N = 50 nucleus 90 Zr was studied in photon-scattering experiments at the electron linear accelerator ELBE with bremsstrahlung produced at kinetic electron energies of 7.9, 9.0, and 13.2 MeV. We identified 189 levels up to an excitation energy of 12.9 MeV. Statistical methods were applied to estimate intensities of inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. In this way we derived the photoabsorption cross section up to the neutron-separation energy. This cross section matches well the photoabsorption cross section obtained from (γ, n) data and thus provides information about the extension of the dipole-strength distribution toward energies below the neutron-separation energy. An enhancement of E1 strength has been found in the range of 6 MeV to 11 MeV. Calculations within the framework of the quasiparticle-phonon model ascribe this strength to a vibration of the excessive neutrons against the N = Z neutron-proton core, giving rise to a pygmy dipole resonance.

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Pygmy dipole strength close to particle-separation energies—The case of the Mo isotopes

Rusev¹,

Grosse²,

Erhard³

et al.

The 2nd International Conference on Nuclear Physics in Astrophysics

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Abstract. The distribution of electromagnetic dipole strength in 92, 98, 100 Mo has been investigated by photon scattering using bremsstrahlung from the new ELBE facility. The experimental data for well separated nuclear resonances indicate a transition from a regular to a chaotic behaviour above 4 MeV of excitation energy. As the strength distributions follow a Porter-Thomas distribution much of the dipole strength is found in weak and in unresolved resonances appearing as fluctuating cross section. An analysis of this quasi-continuum -here applied to nuclear resonance fluorescence in a novel way -delivers dipole strength functions, which are combining smoothly to those obtained from (γ, n)-data. Enhancements at 6.5 MeV and at ∼ 9 MeV are linked to the pygmy dipole resonances postulated to occur in heavy nuclei.PACS. 21.10. .+k Dipole strength in heavy nucleiThe response of nuclei to dipole radiation is of special importance for the synthesis of the chemical elements in the cosmos: Particle thresholds may be crossed in hot or explosive scenarios leading to the production of new nuclides from previously formed heavier ones by dissociation in the thermal photon bath. This is likely to be the main path for the generation of the approximately 30 -40 neutrondeficient nuclides which cannot be produced in neutron capture reactions [1]. For the understanding and modelling of this so-called p-process the dipole strength function up to and near the particle thresholds has to be known accurately [2]. As shown previously [3], details of the dipole strength (now in n-rich nuclei) may as well have large consequences for the r-process path and also s-process branchings are influenced by nuclear excitations [4] induced by thermal photons. The experimental knowledge [5] on dipole strength is reasonably well established for many heavy and medium mass nuclei in the region of the giant dipole resonance (GDR) by (γ, xn) studies, which often also cover the region directly above the neutron threshold S n . At lower energies three features have been discussed to be of importance for processes in high-temperature cosmic environments: a) the fall-off [6-9] of the E1-strength on the low-energy slope of the GDR; b) the E1-strength between the ground-state (gs) and low energy excitations and its proper extension [10-12] into the regime (a); c) the occurrence of additional pygmy-resonances, [3,[13][14][15], which are assumed to be not as broad as the GDR, but wider as compared to the average level distance D -thus forming an intermediate structure enclosing many levels. Their low energy may well enhance their contribution to photo-dissociation processes in spite of their relatively low strength as compared to the GDR. In principle, also M1-transitions contribute to the dipole strength, but the average M1 strength is typically 1-2 orders of magnitude smaller as compared to E1, and they are frequently [1-3] not taken into account. A further approximation has to be introduced to estimate dipole strengths for transitions not connected to the g...

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Photon scattering fromZr90below neutron emission threshold

Cited by 23 publications

References 16 publications

Evidence for radiative coupling of the pygmy dipole resonance to excited states

Evidence for radiative coupling of the pygmy dipole resonance to excited states

Pygmy dipole strength inZr90

Pygmy dipole strength close to particle-separation energies—The case of the Mo isotopes

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