In a recent Physical Review Letters paper (“Strong evidence for 9N and the limits of existence of atomic nuclei”), scientists from Washington University in St. Louis, Fudan University in China, Western Michigan University, the University of Connecticut, the Chinese Academy of Sciences, and FRIB present strong evidence for a new light isotope of nitrogen: nitrogen-9. Physical Review Letters also highlighted the paper as an Editor’s Suggestion.

With only two neutrons to its seven protons, nitrogen-9 represents the first known case of a nucleus that decays by emitting five protons from its ground-state. The highly ephemeral nitrogen-9 nuclide is located on the very proton-rich edge of the Chart of Nuclides and is close to the limit of what can be considered a nuclear state. It can be viewed as five unbound protons which surround an alpha-particle (a tightly-bound grouping of two protons and two neutrons). This ensemble is briefly held together by their mutual interactions. The unbound protons are liberated in steps, with an initial single proton escaping followed by the simultaneous emission of a first, and then slightly later, a second pair of protons.

The experimental evidence was obtained from data collected at the National Superconducting Cyclotron Laboratory. The authors stated that the existence of such an exotic system is a good test of the quantum mechanics of open or unbound many-body systems. An open-quantum-system calculation using the complex-energy Gamow Shell Model explains the elusive nature of nitrogen-9.

This material is based upon work supported by the U.S. Department of Energy Office of Science Office of Nuclear Physics, the U.S. National Science Foundation, the National Key Research and Development Program of China, and the National Natural Science Foundation of China.

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), supporting the mission of the DOE-SC Office of Nuclear Physics. 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.