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Background: Little data is available for the pygmy dipole resonance (PDR) in axially deformed nuclei. Photon scattering experiments are complicated by high level densities in the PDR region and the small energy difference of transitions to the ground state and to excited states. Purpose: We report on an experimental study of the low-energy dipole strength distribution of the well-deformed nucleus 164Dy between 4.0β7.7 MeV. Methods: The low-lying photoresponse of 164Dy has been investigated using the method of nuclear resonance fluorescence using a quasimonochromatic linearly polarized Ξ³ -ray beam in the energy range of 4.0β7.7 MeV in steps of 0.2 MeV. Results: For excitation energies between 4 MeV and 5 MeV, sufficiently low level densities allow for the identification of individual states, including level energies, reduced transition widths and branching ratios. Energy-averaged mean decay branching ratios, mean population ratios and partial absorption cross sections were determined above 5 MeV up to the neutron-separation threshold at 7.7 MeV. A Lorentzian-shaped enhancement of the partial photo absorption cross section followed by decays back to the ground-state band is found at 6.10(5) MeV with a width of 0.77(23) MeV. A comparison with results from complementary measurements is performed using the framework of the statistical model. Conclusions: The experimental results for the mean population ratios deviate systematically from the statistical model simulation by 30(6)%. However, they are in agreement within one standard deviation of the simulation.
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Systematic study of the low-lying electric dipole strength in Sn isotopes and its astrophysical implications
The πΎ-ray strength functions (GSFs) and nuclear level densities (NLDs) below the neutron threshold have been extracted for 111β113,116β122,124Sn from particle-πΎ coincidence data with the Oslo method. The evolution of bulk properties of the low-lying electric dipole response has been investigated on the basis of the Oslo GSF data and results of a recent systematic study of electric- and magnetic dipole strengths in even-even Sn isotopes with relativistic Coulomb excitation. The obtained GSFs reveal a resonance-like peak on top of the tail of the isovector giant dipole resonance centered at β8 MeV and exhausting β2% of the classical Thomas-Reiche-Kuhn (TRK) sum. For mass numbers β₯118 the data suggest also a second peak centered at β6.5 MeV. It corresponds to 0.1%β0.5% of the TRK sum rule and shows an approximate linear increase with the mass number. In contrast with predictions of the relativistic quasiparticle random-phase and time-blocking approximation calculations, no monotonic increase in the total low-lying πΈβ’1 strength was observed in the experimental data from 111Sn to 124Sn, demonstrating rather similar strength distributions in these nuclei. The Oslo GSFs and NLDs were further used as inputs to constrain the cross sections and Maxwellian-averaged cross sections of (π,πΎ) reactions in the Sn isotopic chain using talys. The obtained results agree well with other available experimental data and the recommended values from the JINA REACLIB, BRUSLIB, and KADoNiS libraries. Despite relatively small exhausted fractions of the TRK sum rule, the low-lying electric dipole strength makes a noticeable impact on the radiative neutron-capture cross sections in stable Sn isotopes. Moreover, the experimental Oslo inputs for the 121,123Sn β’(π,πΎ)β’ 122,124Sn reactions were found to affect the production of Sb in the astrophysical π process, providing new constraints on the uncertainties of the resulting chemical abundances from multizone low-metallicity asymptotic giant branch stellar models.
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- PAR ID:
- 10512315
- Editor(s):
- na
- Publisher / Repository:
- American Physical Society
- Date Published:
- Journal Name:
- Physical Review C
- Edition / Version:
- 1
- Volume:
- 109
- Issue:
- 5
- ISSN:
- 2469-9985
- Page Range / eLocation ID:
- 1-25
- Subject(s) / Keyword(s):
- Nuclear dipole strength functions, level density, experiment and theory, relativistic response theory
- Format(s):
- Medium: X Size: 3.9MB Other: pdf
- Size(s):
- 3.9MB
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1103/PhysRevC.109.054311
