Neutron Capture and the Antineutrino Yield from Nuclear Reactors.

Area of Science:

• Nuclear Physics
• Reactor Physics
• Particle Physics

Background:

• Antineutrino spectra from nuclear reactors are crucial for reactor monitoring and fundamental physics research.
• Existing models primarily assume a linear relationship between fission rate and antineutrino production.

Purpose of the Study:

• To identify and quantify a previously unrecognized, flux-dependent correction to the antineutrino spectrum from nuclear reactors.
• To develop a model for this nonlinear correction and validate it with reactor simulations.

Main Methods:

• Identification of specific nuclides with nonlinear dependence of decay chains on neutron flux.
• Development of an analytic model to quantify the antineutrino spectral correction.
• Comparison of model predictions with detailed simulations of various nuclear reactors.

Main Results:

• Discovered four nonlinear nuclides contributing to an antineutrino excess below 3.2 MeV.
• The correction is dependent on reactor thermal neutron flux.
• In a typical pressurized water reactor, the correction reaches ~0.9% of the low-energy flux.
• For naval reactors, this correction can reach 5% by the end of cycle.

Conclusions:

• A significant, flux-dependent correction to the reactor antineutrino spectrum exists due to nonlinear nuclides.
• This correction is comparable to other known low-energy spectral corrections.
• Accurate reactor antineutrino spectrum modeling requires incorporating this nonlinear effect, especially for low-energy applications and reactor monitoring.