Scientists Solve Decades-Old Atomic Nuclei Mystery

According to a study published July 15, 2026, in Nature, researchers at the Facility for Rare Isotope Beams (FRIB) have discovered that unexpected low-energy gamma rays in zinc-70 originate from magnetic transitions hidden inside the nucleus, resolving a decades-long nuclear physics puzzle regarding how atomic nuclei emit electromagnetic radiation.

FRIB Experiment Traces Zinc-70 Gamma-Ray Anomaly

For decades, experiments consistently revealed an unexpected surge in low-energy gamma rays emitted by certain nuclei. This phenomenon, known as the low-energy enhancement (LEE), appeared within the gamma-ray strength function, yet its physical origin remained a mystery to researchers, according to findings led by a multi-institutional collaboration across 25 institutions. Theory failed to predict the anomaly. “This low-energy enhancement wasn’t predicted by theory, so it was kind of a shock to the community when it was first observed,” said Eleanor Ronning, lead author of the study, former FRIB graduate student, and now a postdoctoral research fellow at the National Institute for Nuclear Physics in Padova, Italy. The breakthrough came when the international team focused their investigation on zinc-70, a nucleus whose known energy levels are well documented.

Using LEBIT and Isomer Separation to Isolate Signals

To capture the elusive weak signal without background noise interference, the research team utilized FRIB’s Low Energy Beam and Ion Trap (LEBIT), a high-precision mass spectrometer. According to Ryan Ringle, associate professor of physics at FRIB and LEBIT group leader, the facility separated nuclei with extremely small differences in mass and energy. Rather than using a single route to produce zinc-70, the team examined the beta decay of two distinct states of its parent nucleus, copper-70. One copper-70 beam held nuclei in the ground state, while the other contained nuclei in an excited state known as an isomer. By employing the beta-Oslo method and the Shape method to calculate the gamma-ray strength function recorded by the Summing NaI (SuN) detector, researchers conclusively proved that magnetic transitions generate the low-energy enhancement inside zinc-70.

Impact on Astrophysical Element Formation Models

Uncovering the origin of the low-energy enhancement directly impacts calculations used to understand stellar nuclear processes and the formation of elements in space. According to the research group, LEE increases the expected frequency of neutron-capture reactions, where an atomic nucleus absorbs a neutron. These specific reactions drive the production of heavy elements during catastrophic cosmic events like supernova explosions and neutron star mergers. When LEE affects numerous nuclei, its combined influence alters calculated reaction rates across stellar models, nuclear energy systems, and applications tied to the National Nuclear Security Administration’s work, as noted by Andrea Richard, co-lead of the study and assistant professor and interim director of the Edwards Accelerator Laboratory at Ohio University.

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