Test of the Brink-Axel Hypothesis for the Pygmy Dipole Resonance

Martin, Dirk; Neumann-Cosel, P. von; Tamii, A.; Aoi, N.; Bassauer, S.; Bertulani, C. A.; Carter, J.; Donaldson, L. M.; Fujita, H.; Fujita, Y.; Hashimoto, Takashi; Hatanaka, K.; Ito, Tomoko; Krugmann, A.; Liu, B.; Maeda, Y.; Miki, K.; Neveling, R.; Pietralla, N.; Poltoratska, I.; Ponomarev, V. Yu.; Richter, A.; Shima, T.; Yamamoto, Tetsuya; Zweidinger, M.

doi:10.1103/physrevlett.119.182503

Cited by 40 publications

(65 citation statements)

References 56 publications

(81 reference statements)

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“…The validity of the Brink-Axel hypothesis was recently proven for the case of 96 Mo on the basis of a comparison of new (p, p ′ ) data [53] with existing ( 3 He, 3 He') data [54] and (γ, γ ′ ) data [32]. Similar to the present cases of 206 Pb and 208 Pb, the ( 3 He, 3 He') data are close to the (γ, γ ′ ) data between about 7.3 and 8.5 MeV, but drop rapidly toward low energy.…”

Section: A Photoabsorption Cross Section Of 206 Pbmentioning

confidence: 98%

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Dipole strength distribution in Pb206 for the evaluation of the neutron capture cross section of Pb205

Shizuma¹,

Iwamoto²,

Makinaga³

et al. 2018

Phys. Rev. C

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The dipole strength distribution of 206 Pb was investigated via a nuclear resonance fluorescence experiment using bremsstrahlung produced with an electron beam at a kinetic energy of 10.5 MeV at the linear accelerator ELBE. We identified 88 states resonantly excited at energies from 3.7 to 8.2 MeV. The analysis of the measured γ-ray spectra includes the quasicontinuum of levels at high energy. Monte Carlo simulation of γ-ray cascades were performed to obtain the intensities of inelastic transitions and branching ratios of the ground state transitions. The extracted photo-absorption cross section show enhanced dipole strength at the excitation energies around 5.5 and 7 MeV, which may related to a pygmy dipole resonance. The present (γ, γ′) data combined with (γ, n) data from the literature were used for confining input parameters of the statistical calculation code CCONE to derive the neutron capture cross section of the unstable 205 Pb nucleus.

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Section: A Photoabsorption Cross Section Of 206 Pbmentioning

confidence: 98%

“…However, the authors of Ref. [53] state that an apparent violation of the Brink-Axel hypothesis was suggested by the (γ, γ ′ ) data in Ref. [32].…”

Section: A Photoabsorption Cross Section Of 206 Pbmentioning

confidence: 99%

Dipole strength distribution in Pb206 for the evaluation of the neutron capture cross section of Pb205

Shizuma¹,

Iwamoto²,

Makinaga³

et al. 2018

Phys. Rev. C

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“…In Fig. 6, the BSk27 + QRPA photon strength functions are compared with experimental E 1 data at low energies available from nuclear resonance fluorescence (NRF) [41,42] and proton scattering [43][44][45] experiments. A relatively good agreement between theory and experiment can be seen in Fig.…”

Section: Comparison With Experimental Datamentioning

confidence: 99%

Systematical studies of theE1photon strength functions combining the Skyrme-Hartree-Fock-Bogoliubov plus quasiparticle random-phase approximation model and experimental giant dipole resonance properties

Goriely²,

Khan³

2021

Phys. Rev. C

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Valuable theoretical predictions of nuclear dipole excitations in the whole nuclear chart are of great interest for different applications, including in particular nuclear astrophysics. We present here the systematic study of the electric-dipole (E 1) photon strength functions combining the microscopic Hartree-Fock-Bogoliubov plus quasiparticle random-phase approximation (HFB + QRPA) model and the parametrizations constrained by the available experimental giant dipole resonance (GDR) data. For about 10 000 nuclei with 8 Z 124 lying between the proton and the neutron drip-lines on nuclear chart, the particle-hole (ph) strength distributions are computed using the HFB + QRPA model under the assumption of spherical symmetry and making use of the BSk27 Skyrme effective interaction derived from the most accurate HFB mass model (HFB-27) so far achieved. Large-scale calculations of the BSk27 + QRPA E 1 photon strength functions are performed in the framework of a specific folding procedure describing the damping of nuclear collective motion empirically. In particular, three phenomenological improvements are considered in this folding procedure. First, two interference factors are introduced and adjusted to reproduce at best the available experimental GDR data. Second, an empirical expression accounting for the deformation effect is applied to describe the peak splitting of the strength function. Third, the width of the strength function is corrected by a temperature-dependent term, which effectively increases the deexcitation photon strength function at low energy. The theoretical E 1 photon strength functions as well as the extracted GDR peaks and widths are comprehensively compared with available experimental data. A relatively good agreement with data indicates the reliability of the present calculations. Eventually, the astrophysical rates of (n, γ ) reactions for all the 10 000 nuclei with 8 Z 124 lying between the proton and the neutron drip lines are estimated using the present E 1 photon strength functions. The resulting reaction rates are compared with the previous BSk7 + QRPA results as well as the Gogny-HFB + QRPA predictions based on the D1M interaction.

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“…Results of γ -ray induced measurements [17]-used as input for statistical model calculationswere not able to reproduce the partial cross sections of the 89 Y(p, γ ) reactions via the statistical model [18]. Deviations between different experimental techniques were also reported for 120 Sn [25], while in the case of 96 Mo [16] various methods seem to agree. Furthermore, a new method using the (γ , γ γ ) reactions has revealed inconsistencies in the extraction of γ -strength function values in 128 Te from different excitation energies pointing to a violation of the generalized Brink-Axel hypothesis in that specific case [21].…”

Section: Introductionmentioning

confidence: 96%

“…Moreover, dependencies in the extraction of the γ -ray strength function from experimental data on other nuclear physics parameters, such as nuclear level densities or spin distributions, need to be minimized and to be under control. Throughout the last years, many techniques have been developed and improved (see [15][16][17][18][19][20][21][22][23][24][25][26][27][28] and references therein) to investigate γ -strength functions above and below the particleseparation energies. All of these approaches are to some extent selective regarding their excitation mechanism and some rely on theoretical modeling in the determination of the γ -strength function.…”

Section: Introductionmentioning

confidence: 99%

Primary γ -ray intensities and γ -strength functions from discrete two-step γ -ray cascades in radiative proton-capture experiments

et al. 2020

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Background: Reaction rates of radiative capture reactions can play a crucial role in the nucleosynthesis of heavy nuclei in explosive stellar environments. These reaction rates depend strongly on γ -ray decay widths in the reaction products, which are, for nonresonant capture reactions at high excitation energies, derived from the γ -ray strength function and the nuclear level density. Recently, the ratio method was applied to primary γ rays observed from (d, p) reactions and nuclear resonance fluorescence measurements to extract the dipole strength in atomic nuclei and to test the generalized Brink-Axel hypothesis. Purpose: The purpose of this work is to apply the ratio method to primary γ -ray intensities of the 63,65 Cu(p,γ ) reactions to extract γ -ray strength information on the nuclei 64,66 Zn. The impact of spin distribution, total γ -ray decay widths, level densities, and width fluctuations on the application of the ratio method will be discussed. Additionally, by comparing the relative γ -ray strength at different excitation energies, conclusions on the validity of the generalized Brink-Axel hypothesis can be made. Method: The radiative proton capture reaction measurements have been performed at the HORUS γ -ray spectrometer of the University of Cologne at one excitation energy for each reaction. Primary γ -ray intensities have been determined by normalizing secondary γ -ray transitions in two-step cascades using their absolute branching ratio. The ratio method was applied to the measured primary γ -ray intensities as well as to previous measurements by Erlandsson et al. at different excitation energies. Results: The relative strength function curve for 64 Zn from our measurement shows no significant deviation from the previous measurement at a different excitation energy. The same is true for 66 Zn where both measurements were at almost the same excitation energy. Absolute γ -strength function values have been obtained by normalizing the relative curves to quasiparticle random phase approximation calculations because of the absence of experimental data in the respective energy region. Conclusion:The generalized Brink-Axel hypothesis, i.e., the independence of the strength function on the excitation energy, seems to hold in the studied energy region and nuclei. The method to obtain primary γ -ray intensities from two-step cascade spectra was shown to be a valuable and sensitive tool although its uncertainties are connected to the knowledge of the low-energy level scheme of the investigated nucleus. The scaling in the ratio method should be taken with care, because the relative strength is not a simple sum of f E 1 and f M1 but a somewhat complex linear combination dependent on the excitation energy of the nucleus.

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Test of the Brink-Axel Hypothesis for the Pygmy Dipole Resonance

Cited by 40 publications

References 56 publications

Dipole strength distribution in Pb206 for the evaluation of the neutron capture cross section of Pb205

Dipole strength distribution in Pb206 for the evaluation of the neutron capture cross section of Pb205

Systematical studies of theE1photon strength functions combining the Skyrme-Hartree-Fock-Bogoliubov plus quasiparticle random-phase approximation model and experimental giant dipole resonance properties

Primary γ -ray intensities and γ -strength functions from discrete two-step γ -ray cascades in radiative proton-capture experiments

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