Magnetic Flips Inside Atomic Nuclei Solve Decades-Old Gamma Ray Mystery

For decades, nuclear physicists have been confronted with a persistent anomaly that their models could not explain. When certain atomic nuclei undergo radioactive decay, they emit an unexpectedly high number of low-energy gamma rays. This phenomenon, known as the "low-energy enhancement" (LEE), was not predicted by standard theoretical frameworks, leaving researchers unable to anticipate which nuclei would exhibit the glow and why it was happening in the first place.[1][2]

Now, an international team of scientists led by the Facility for Rare Isotope Beams (FRIB) and Lawrence Livermore National Laboratory (LLNL) has finally identified the source of the mysterious signal. In a study published in the journal Nature, the researchers demonstrated that the excess gamma rays are produced by magnetic transitions occurring deep inside the nucleus.[1][5]

Gamma rays are a form of electromagnetic radiation released when an excited atomic nucleus transitions to a lower, more stable energy state. These transitions are generally classified as either electric or magnetic, reflecting the different ways protons and neutrons reorganize themselves before releasing the energy.[3][6]

To isolate the cause of the LEE, the research team focused on zinc-70, a nucleus known to exhibit the enhancement. Using specialized instruments at FRIB, they examined the beta decay of copper-70 into zinc-70 through two distinct pathways—one from the copper's ground state and another from an excited isomeric state.[4][5]

This dual-pathway approach allowed the scientists to separate electric and magnetic decay states. They observed that during an electric transition, protons inside the nucleus shifted their physical positions. However, during a magnetic transition, the neutrons and protons essentially flipped their internal magnets.[1][2]

The experiment revealed that only the magnetic transition produced the low-energy enhancement in gamma rays. "This is a key step forward," said Andrea Richard, co-lead of the study and an assistant professor at Ohio University. "We now have a consistent explanation that connects experimental observations with theory."[2][4]

The discovery has profound implications for astrophysics, particularly in understanding how the universe builds heavy elements. The low-energy enhancement increases the frequency of neutron-capture reactions beyond standard predictions.[1][4]

These reactions are the primary engine for forging heavy elements during extreme cosmic events, such as supernovae and the collisions of neutron stars. By accounting for the magnetic flips that drive the LEE, astrophysicists can drastically improve their calculations of reaction rates in these stellar environments.[1][4]

Beyond the cosmos, the findings will also refine practical applications on Earth. Improved nuclear models will enhance the interpretation of past test program results, bolster nuclear forensics capabilities, and inform the development of next-generation nuclear energy systems.[2][3]