Magnetic Signals in Nuclei Reveal How Stars Build Chemical Elements

EAST LANSING, Mich. — A new Nature study reports that a long-mysterious surplus of faint, low-energy gamma rays emitted by zinc-70 is not a statistical quirk, but a signature of magnetism inside the nucleus. The finding helps solve a decades-old puzzle in nuclear physics and could reshape how scientists model reactions that forge elements in extreme astrophysical environments.

Gamma rays act like fingerprints of how nuclei shed energy after being excited. The probability of emitting gamma rays at different energies is summarized by the gamma-ray strength function, a key ingredient used in calculations ranging from laboratory experiments to astrophysical rate predictions. For years, researchers have seen a “low-energy enhancement” (LEE): unexpectedly more gamma rays at the low end of the spectrum than conventional expectations anticipate.

Crucially, the team demonstrates that the excess is tied to magnetic transitions, clarifying what type of nuclear rearrangement is responsible. Electric and magnetic transitions reflect different ways protons and neutrons reorganize as the nucleus moves between energy states, and LEE had been difficult to attribute to either mechanism.

The work used an experimental strategy that begins with beta decay of copper-70, preparing zinc-70 through two distinct initial pathways. By separating copper-70’s ground-state and isomeric-state contributions, the researchers effectively create two complementary “entry routes” into the same nucleus, which improves sensitivity to the structure of zinc-70’s low-energy gamma emissions.

To produce exceptionally pure isomer-separated beams, the collaboration leveraged FRIB’s Low Energy Beam and Ion Trap (LEBIT). The resulting gamma rays from zinc-70 were then captured with the Summing NaI (SuN) detector, enabling precise reconstruction of how the strength function varies with energy.

Instead of relying on a single analysis, the team applied two established extraction approaches—the beta-Oslo method and the Shape method—to independently determine the gamma-ray strength function for each initial state. When the results were compared, magnetic transitions consistently emerged as the driver of the enhancement.

“This is a key step forward,” the researchers note, because it connects the experimental anomaly directly to a theoretical explanation. That means LEE can be treated as a physical mechanism rather than an unresolved systematic effect.

Beyond the nucleus, the implications are practical: LEE increases the likelihood of neutron-capture reactions, influencing the formation of heavy elements during events like supernovae and neutron star mergers. Over many nuclei, even subtle changes can significantly shift reaction-rate estimates used in both astrophysics modeling and nuclear technology planning.

Finally, the study showcases the role of next-generation tools and cross-institution collaboration. By combining FRIB’s rare-isotope capabilities with multi-lab analysis expertise, the researchers also point to a roadmap for extending isomer-separated measurements to other nuclei to map where LEE appears—and why.

Keywords

Gamma rays; nuclear structure; zinc-70; low-energy enhancement; magnetic transitions; gamma-ray strength function; beta decay; isomer separation; neutron capture; astrophysics