Recent experimental discoveries are reshaping how scientists view atomic nuclei. Traditionally, nuclei have been classified as either stable or unstable, but this binary distinction overlooks the wide range of nuclear lifetimes, from fleeting moments to times far exceeding the age of the universe. Witek Nazarewicz, John A. Hannah Distinguished Professor of Physics and chief scientist at FRIB, and Lee Sobotka, professor of chemistry and physics at Washington University in St. Louis, wrote an article (“The lessons learned from ephemeral nuclei”) about the discoveries for Physics Today.
Atomic nuclei are composed of protons and neutrons, which are held together by the strong force. Of the roughly 8,000 known nuclei in the Chart of Nuclides, categorized by their number of protons and neutrons, only about 300 are stable and can be found on Earth. Most nuclei studied in laboratories such as FRIB are unstable, short-lived, and decay through processes like alpha decay, beta decay and electron capture, and spontaneous fission.
In recent years, researchers have focused on ephemeral nuclei—nuclei with incredibly short lifetimes that are barely held together. These fleeting nuclear states challenge conventional definitions of what constitutes a nucleus and offer valuable insights into both nuclear astrophysics and diverse exotic environments. Advanced techniques like invariant-mass spectroscopy are helping scientists unravel the complex decay sequences of these unstable nuclei. This research is pushing the boundaries of nuclear physics and offering potential breakthroughs in our understanding of the universe. In addition, the lessons learned from the study of nuclei with fleeting lifetimes can be applied to atomic, molecular, and reduced-dimensionality open quantum systems.
”One of the goals of the research program at FRIB is to discover exotic nuclides with extreme neutron-to-proton ratios, including the ephemeral ones. These discoveries will revolutionize our knowledge about nuclear science and nuclear astrophysics,” said Nazarewicz. “The methods developed to produce nuclei at the edge of the chart also improve the ability to create much longer-lived unstable nuclei that lie closer to the valley of stability.”
Michigan State University (MSU) operates the Facility for Rare Isotope Beams (FRIB) as a user facility for the U.S. Department of Energy Office of Science (DOE-SC), with financial support from and furthering the mission of the DOE-SC Office of Nuclear Physics. Hosting the most powerful heavy-ion accelerator, FRIB enables scientists to make discoveries about the properties of rare isotopes in order to better understand the physics of nuclei, nuclear astrophysics, fundamental interactions, and applications for society, including in medicine, homeland security, and industry. User facility operation is supported by the DOE-SC Office of Nuclear Physics as one of 28 DOE-SC user facilities.
The U.S. Department of Energy Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of today’s most pressing challenges. For more information, visit energy.gov/science.