Surprising patterns challenge long-held nuclear theory

Los Alamos scientists studying how atoms “catch” neutrons have found repeating patterns where long-standing theory predicted only randomness. These patterns — which were observed in a sizable number of nuclei — suggest that a physical mechanism is missing from current nuclear physics models. 
 
Read the paper 
 
Why this matters: The finding reveals gaps in a long-standing theory that pervades the physics of virtually all complex systems, including nuclear reactions.

• Data from neutron capture cross sections — the measured likelihood that a nucleus absorbs a passing neutron — are essential to applications ranging from nuclear energy and national security to astrophysics. For example, accounting for the correlations within and between key nuclear reactions is crucial for improving the reliability of criticality calculations for national security and nuclear energy applications.
• The observed repeating patterns, or oscillations, are new correlations that may significantly impact these calculations and point to missing physics and the need for more accurate theories.

What’s next: To uncover the physical mechanisms behind the oscillations and guide new physics models, the authors suggest applying their method to more isotopes, extending the approach beyond neutron capture to fission, where preliminary signs of oscillations already appear. Such steps could expand the number and precision of tests of nuclear theory, while also pointing the way to deeper insights into how nuclei interact with neutrons.

About the science: Los Alamos has long been a leader in nuclear data generation and analysis. Inspired by nonstatistical effects revealed by data from other LANSCE experiments (e.g., DICER), the researchers performed a systematic study on other nuclei, which indicated the oscillating cross sections. 

Funding: This work was supported in part by the National Nuclear Security Administration’s Nuclear Criticality Safety Program.

LA-UR-25-31133