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The concept of nuclear photon strength functions: A model-independent approach via (γ→,γγ) reactions

Publication ,  Journal Article
Isaak, J; Savran, D; Löher, B; Beck, T; Bhike, M; Gayer, U; Krishichayan, ; Pietralla, N; Scheck, M; Tornow, W; Werner, V; Zilges, A; Zweidinger, M
Published in: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
January 10, 2019

Most theoretical approaches used in nuclear astrophysics to model the nucleosynthesis of heavy elements incorporate the so-called statistical model in order to describe the excitation and decay properties of atomic nuclei. One of the basic assumptions of this model is the validity of the Brink–Axel hypothesis and the related concept of so-called photon strength functions to describe γ-ray transition probabilities. We present a novel experimental approach that allows for the first time to experimentally determine the photon strength function simultaneously in two independent ways by a unique combination of quasi-monochromatic photon beams and a newly implemented γ–γ coincidence setup. This technique does not assume a priori the validity of the Brink–Axel hypothesis and sets a benchmark in terms of the detection sensitivity for measuring decay properties of photo-excited states below the neutron separation energy. The data for the spherical off-shell nucleus 128Te were obtained for γ-ray beam-energy settings between 3 MeV and 9 MeV in steps of 130 keV for the lower beam energies and in steps of up to 280 keV for the highest beam settings. We present a quantitative analysis on the consistency of the derived photon strength function with the Brink–Axel hypothesis. The data clearly demonstrate a discrepancy of up to a factor of two between the photon strength functions extracted from the photoabsorption and photon emission process, respectively. In addition, we observe that the photon strength functions are not independent of the excitation energy, as usually assumed. Thus, we conclude, that the Brink–Axel hypothesis is not strictly fulfilled in the excitation-energy region below the neutron separation threshold (Sn=8.78MeV) for the studied case of 128Te.

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Published In

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

DOI

ISSN

0370-2693

Publication Date

January 10, 2019

Volume

788

Start / End Page

225 / 230

Related Subject Headings

  • Nuclear & Particles Physics
  • 51 Physical sciences
  • 49 Mathematical sciences
  • 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics
  • 0201 Astronomical and Space Sciences
  • 0105 Mathematical Physics
 

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Isaak, J., Savran, D., Löher, B., Beck, T., Bhike, M., Gayer, U., … Zweidinger, M. (2019). The concept of nuclear photon strength functions: A model-independent approach via (γ→,γγ) reactions. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 788, 225–230. https://doi.org/10.1016/j.physletb.2018.11.038
Isaak, J., D. Savran, B. Löher, T. Beck, M. Bhike, U. Gayer, U. Krishichayan, et al. “The concept of nuclear photon strength functions: A model-independent approach via (γ→,γγ) reactions.” Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 788 (January 10, 2019): 225–30. https://doi.org/10.1016/j.physletb.2018.11.038.
Isaak J, Savran D, Löher B, Beck T, Bhike M, Gayer U, et al. The concept of nuclear photon strength functions: A model-independent approach via (γ→,γγ) reactions. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. 2019 Jan 10;788:225–30.
Isaak, J., et al. “The concept of nuclear photon strength functions: A model-independent approach via (γ→,γγ) reactions.” Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, vol. 788, Jan. 2019, pp. 225–30. Scopus, doi:10.1016/j.physletb.2018.11.038.
Isaak J, Savran D, Löher B, Beck T, Bhike M, Gayer U, Krishichayan, Pietralla N, Scheck M, Tornow W, Werner V, Zilges A, Zweidinger M. The concept of nuclear photon strength functions: A model-independent approach via (γ→,γγ) reactions. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. 2019 Jan 10;788:225–230.
Journal cover image

Published In

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

DOI

ISSN

0370-2693

Publication Date

January 10, 2019

Volume

788

Start / End Page

225 / 230

Related Subject Headings

  • Nuclear & Particles Physics
  • 51 Physical sciences
  • 49 Mathematical sciences
  • 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics
  • 0201 Astronomical and Space Sciences
  • 0105 Mathematical Physics