The concept of nuclear photon strength functions: A model-independent approach via ((gamma)over-right-arrow, gamma ' gamma '') reactions

a model-independent approach via (gamma, gamma'gamma'') reactions

J. Isaak, D. Savran, B. Loeher, T. Beck, M. Bhike, U. Gayer, Krishichayan, N. Pietralla, M. Scheck, W. Tornow, V. Werner, A. Zilges, M. Zweidinger

Research output: Contribution to journalArticle

23 Downloads (Pure)

Abstract

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 () for the studied case of 128Te.
Original languageEnglish
Pages (from-to)225-230
Number of pages6
JournalPhysics Letters B
Volume788
Early online date22 Nov 2018
DOIs
Publication statusPublished - 10 Jan 2019

Fingerprint

photons
excitation
rays
energy
neutrons
nuclear astrophysics
nuclei
photon beams
photoabsorption
decay
heavy elements
nuclear fusion
transition probabilities
quantitative analysis
thresholds

Keywords

  • Photon strength function
  • Statistical model
  • γ-ray spectroscopy
  • γ–γ coincidence experiments

Cite this

Isaak, J. ; Savran, D. ; Loeher, 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 ((gamma)over-right-arrow, gamma ' gamma '') reactions : a model-independent approach via (gamma, gamma'gamma'') reactions. In: Physics Letters B. 2019 ; Vol. 788. pp. 225-230.
@article{97cf577064cc4b60a9607068ad856f89,
title = "The concept of nuclear photon strength functions: A model-independent approach via ((gamma)over-right-arrow, gamma ' gamma '') reactions: a model-independent approach via (gamma, gamma'gamma'') reactions",
abstract = "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 () for the studied case of 128Te.",
keywords = "Photon strength function, Statistical model, γ-ray spectroscopy, γ–γ coincidence experiments",
author = "J. Isaak and D. Savran and B. Loeher and T. Beck and M. Bhike and U. Gayer and Krishichayan and N. Pietralla and M. Scheck and W. Tornow and V. Werner and A. Zilges and M. Zweidinger",
year = "2019",
month = "1",
day = "10",
doi = "10.1016/j.physletb.2018.11.038",
language = "English",
volume = "788",
pages = "225--230",
journal = "Physics Letters B",
issn = "0370-2693",
publisher = "Elsevier B.V.",

}

The concept of nuclear photon strength functions: A model-independent approach via ((gamma)over-right-arrow, gamma ' gamma '') reactions : a model-independent approach via (gamma, gamma'gamma'') reactions. / Isaak, J.; Savran, D.; Loeher, B.; Beck, T.; Bhike, M.; Gayer, U.; Krishichayan; Pietralla, N.; Scheck, M.; Tornow, W.; Werner, V.; Zilges, A.; Zweidinger, M.

In: Physics Letters B, Vol. 788, 10.01.2019, p. 225-230.

Research output: Contribution to journalArticle

TY - JOUR

T1 - The concept of nuclear photon strength functions: A model-independent approach via ((gamma)over-right-arrow, gamma ' gamma '') reactions

T2 - a model-independent approach via (gamma, gamma'gamma'') reactions

AU - Isaak, J.

AU - Savran, D.

AU - Loeher, B.

AU - Beck, T.

AU - Bhike, M.

AU - Gayer, U.

AU - Krishichayan, null

AU - Pietralla, N.

AU - Scheck, M.

AU - Tornow, W.

AU - Werner, V.

AU - Zilges, A.

AU - Zweidinger, M.

PY - 2019/1/10

Y1 - 2019/1/10

N2 - 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 () for the studied case of 128Te.

AB - 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 () for the studied case of 128Te.

KW - Photon strength function

KW - Statistical model

KW - γ-ray spectroscopy

KW - γ–γ coincidence experiments

U2 - 10.1016/j.physletb.2018.11.038

DO - 10.1016/j.physletb.2018.11.038

M3 - Article

VL - 788

SP - 225

EP - 230

JO - Physics Letters B

JF - Physics Letters B

SN - 0370-2693

ER -