Magnetic transitions inside nuclei explain unexpected low-energy gamma rays

Researchers at the Facility for Rare Isotope Beams (FRIB) have identified the mechanism behind a decades-old puzzle in nuclear physics: why some atomic nuclei emit more low-energy gamma rays than standard models predict. The effect, known as low-energy enhancement, appeared unpredictably across different nuclei and lacked a consistent theoretical explanation.

The study, published in Nature, examined the decay of a radioactive copper isotope into zinc-70 using FRIB's specialized instruments. The experiment separated two distinct decay pathways — one involving an electric transition where protons shift position, and another involving a magnetic transition where protons and neutrons flip their internal magnetic orientations.

Only the magnetic transition produced the unexpected surplus of low-energy gamma rays, demonstrating that the phenomenon is magnetic in nature. Lead author Eleanor Ronning, a former FRIB graduate student, said the enhancement was a shock to the community when first observed because it was not predicted by theory.

Co-lead Andrea Richard, formerly a postdoctoral researcher at Lawrence Livermore National Laboratory (LLNL) and now an assistant professor at Ohio University, said the results provide a consistent explanation linking experimental observations with theory. LLNL scientists contributed expertise and monitored the weeklong, continuous experimental run.

Although the measurement focused on a single nucleus, the researchers say the findings can improve nuclear models across a wider range of elements and reactions. LLNL scientist Darren Bleuel noted that improved theory based on the discovery could enhance stockpile stewardship, nuclear forensics, and modeling of nuclear reactions in stars, supernovae, and neutron star mergers.

The work also has implications for understanding the creation of heavy elements in astrophysical environments and for nuclear energy applications. The journal reference is E. K. Ronning et al., "Magnetic character of the low-energy enhancement in 70Zn," Nature, 2026.