Deviations from the Porter-Thomas Distribution due to Nonstatistical γ Decay below the ^{150}Nd Neutron Separation...

Area of Science:

• Nuclear Physics
• Quantum Mechanics

Background:

• Understanding nuclear decay processes is crucial for nuclear structure physics.
• The Porter-Thomas distribution is a standard model for partial transition widths.

Purpose of the Study:

• To develop and apply a novel method for studying fluctuations in partial transition widths.
• To investigate the validity of the Porter-Thomas distribution in specific nuclear systems.

Main Methods:

• Utilizing nuclear resonance fluorescence experiments with quasimonochromatic, linearly polarized photon beams.
• Analyzing the average branching ratios of gamma decays from J=1 states to the ground and 2_{1}^{+} states in even-even nuclei.
• Comparing experimental results with theoretical predictions based on the chi-squared distribution.

Main Results:

• A constant average branching ratio of 0.490(16) for gamma decays from 1^{-} states in ^{150}Nd between 5 and 7 MeV was observed.
• The derived degree of freedom (ν=1.93(12)) deviates significantly from the value required by the Porter-Thomas distribution (ν=1).
• Non-statistical effects in gamma decay behavior were quantified, ranging from 9.4(10)% to 94(10)%.

Conclusions:

• The study rejects the universal validity of the Porter-Thomas distribution for partial transition widths in the studied energy range.
• Observed deviations indicate the presence and significance of non-statistical effects in nuclear gamma decay.
• The developed method provides a new tool for probing nuclear structure and reaction dynamics.