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The Porter-Thomas distribution (PTD) for neutron widths is challenged by new evidence. We found that coupling to decay channels introduces terms violating orthogonal invariance, modifying the PTD significantly.

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Area of Science:

  • Nuclear physics
  • Quantum mechanics

Background:

  • The Porter-Thomas distribution (PTD) is a fundamental statistical model for describing partial neutron widths.
  • Recent experimental data have raised questions about the validity of the PTD in certain nuclear systems.

Purpose of the Study:

  • To investigate the theoretical basis for deviations from the Porter-Thomas distribution.
  • To identify the physical mechanisms responsible for the observed modifications of the PTD.

Main Methods:

  • Analysis of the effective Hamiltonian in nuclear reactions.
  • Identification of terms violating orthogonal invariance.
  • Calculation of modifications due to coupling to decay channels.

Main Results:

  • Two specific terms in the effective Hamiltonian were identified as violating orthogonal invariance.
  • These terms arise from the coupling to decay channels, including the neutron channel and nonstatistical gamma decays.
  • Realistic estimates show these couplings significantly alter the PTD, aligning with experimental observations.

Conclusions:

  • The deviations from the Porter-Thomas distribution are explained by coupling effects to decay channels.
  • The study provides a theoretical framework to understand and predict modifications to the PTD in nuclear physics.
  • This work reconciles experimental findings with theoretical predictions, enhancing our understanding of nuclear decay processes.