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Deviations from the Porter-Thomas Distribution due to Nonstatistical γ Decay below the Nd150 Neutron Separation Threshold

O. Papst1,*, J. Isaak1,†, V. Werner1, D. Savran2, N. Pietralla1, G. Battaglia3, T. Beck1,‡, M. Beuschlein1, S. W. Finch4,5 et al.

U. Friman-Gayer1,§, K. E. Ide1, R. V. F. Janssens5,6, M. D. Jones5,6, J. Kleemann1, B. Löher2, M. Scheck7,8, M. Spieker9,∥, W. Tornow4,5, R. Zidarova1, and A. Zilges10

  • *Contact author: opapst@ikp.tu-darmstadt.de
  • †Contact author: jisaak@ikp.tu-darmstadt.de
  • ‡Present address: KU Leuven, Instituut voor Kern- en Stralingsfysica, 3001 Leuven, Belgium.
  • §Present address: Vysus Group Sweden AB, 214 21 Malmö, Sweden.
  • ∥Present address: Department of Physics, Florida State University, Tallahassee, Florida 32306, USA.
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Phys. Rev. Lett. 135, 052501 – Published 30 July, 2025

DOI: https://doi.org/10.1103/n6zw-zhz2

Abstract

We introduce a new method for the study of fluctuations of partial transition widths based on nuclear resonance fluorescence experiments with quasimonochromatic linearly polarized photon beams below particle separation thresholds. It is based on the average branching of decays of J=1 states of an even-even nucleus to the 21+ state in comparison to the ground state. Between 5 and 7 MeV, a constant average branching ratio for γ decays from 1− states of 0.490(16) is observed for the nuclide Nd150. Assuming χ2-distributed partial transition widths, this average branching ratio is related to a degree of freedom of ν=1.93(12), rejecting the validity of the Porter-Thomas distribution, requiring ν=1. The observed deviation can be explained by nonstatistical effects in the γ-decay behavior with contributions in the range of 9.4(10)% up to 94(10)%.

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Phys. Rev. Lett. 135, 052501– Published 30 July, 2025
  • Received 1 January 2025
  • Revised 6 March 2025
  • Accepted 20 May 2025
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