Spectral structure of electron antineutrinos from nuclear reactors

Area of Science:

• Nuclear physics
• Reactor physics
• Particle physics

Background:

• Recent measurements of electron antineutrino spectra from nuclear reactors show an unexplained excess of positrons in the 4-6 MeV energy range.
• This discrepancy challenges current theoretical predictions for reactor antineutrino interactions.

Purpose of the Study:

• To investigate the origin of the observed positron energy excess in reactor antineutrino spectra.
• To identify specific nuclear processes and isotopes responsible for spectral anomalies.
• To understand the impact of these spectral substructures on antineutrino measurements.

Main Methods:

• Performed first-principles calculations of fission and beta decay processes in a pressurized water reactor core.
• Analyzed the contributions of prominent fission daughter isotopes to the antineutrino spectrum.
• Investigated Coulomb effects in beta decay to predict spectral substructures.

Main Results:

• Identified prominent fission daughter isotopes as a likely source of the positron energy excess.
• Predicted percent-level substructures within the antineutrino spectrum.
• These substructures are attributed to Coulomb effects during beta decay.

Conclusions:

• Fission daughter isotopes and Coulomb effects are key factors influencing reactor antineutrino spectra.
• Precise measurement of spectral substructures offers insights into nuclear processes within reactors.
• These substructures represent a potential systematic uncertainty for reactor antineutrino experiments.