Researchers at the Facility for Rare Isotope Beams (FRIB), working with colleagues from Lawrence Livermore National Laboratory, have reported findings addressing a long-standing question in nuclear physics regarding anomalous gamma ray emissions from certain atomic nuclei. The research, published in Nature, focuses on a phenomenon known as low-energy enhancement, wherein some nuclei release more low-energy gamma rays than existing theoretical models predicted.
Gamma rays are a type of electromagnetic radiation produced when excited atomic nuclei transition to more stable energy states during radioactive decay. For many decades, scientists observed that specific nuclei emitted unexpectedly large quantities of these low-energy gamma rays, yet this effect could not be reliably predicted or explained through conventional theoretical frameworks. The unpredictability of where this phenomenon occurs presented a significant challenge to the field.
To investigate the mechanism behind this effect, the research team measured gamma rays generated as a radioactive copper isotope decayed into zinc. Using FRIB’s specialized instrumentation, the scientists distinguished between two separate decay pathways and analyzed each independently. The first involved an electric transition, in which protons within the nucleus shifted their positions. The second involved a magnetic transition, where neutrons and protons in the nucleus reoriented their internal magnetic properties. Analysis revealed that only the magnetic transition produced the observed low-energy enhancement, establishing that the phenomenon has a magnetic origin.
The implications of this research extend across multiple scientific domains. Within nuclear security, the improved understanding could enhance assessments of stockpile performance and nuclear forensics capabilities. The findings may also refine models of nuclear reactions occurring in astrophysical environments, including those in stars, supernovae, and neutron star mergers, particularly regarding the creation of heavy elements. Additionally, the improved theoretical framework could benefit nuclear energy applications and broaden understanding across a wider range of nuclear elements and reactions.
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