In a recent Physical Review Letters (PRL) paper, a team of scientists from Argonne National Laboratory, Washington University in St. Louis, the University of Surrey in England, and FRIB explain its new approach to accessing unusual excited nuclear levels.

Atomic nuclei assume discrete energy levels when excited. These energy levels are the nucleus’ unique fingerprint and no two nuclei have identical energy patterns. For exotic nuclei, which often only exist for a fraction of a second, a variety of methods have been devised to measure the energies of their excited levels. Researchers at FRIB have found rather unusual levels formed in the collision of short-lived calcium-38 with a beryllium-9 target at 30-percent of the speed of light when the calcium-38 lost a substantial amount of energy in the encounter.

The unusual excited levels formed in calcium-38 were tracked back to the simultaneous excitation of several protons and neutrons. The energies of such complex states are sensitive probes for nuclear theory. They elude observation in reactions typically performed at high beam energies. Thus, such dissipative scattering reactions are a new tool in the arsenal of researchers that study and model nuclei. In the future, such reactions can be used to study unusual energy levels in many other short-lived nuclei to probe nuclear theory, for example, at the Facility for Rare Isotope Beams.

The authors of the PRL paper include Alexandra Gade, professor of physics at FRIB and in MSU’s Department of Physics and Astronomy and FRIB deputy scientific director; Alex Brown, professor of physics at FRIB and in MSU’s Department of Physics and Astronomy; Dick Weisshaar, senior research physicist; Daniel Bazin, research professor; Kyle Brown, assistant professor of chemistry at FRIB; Peter Farris, graduate assistant; Ava Hill, graduate assistant; Jing Li, former research associate; Brenden Longfellow, former graduate research assistant; and Daniel Rhodes, former graduate assistant.

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; and the Science and Technologies Facilities Council of the United Kingdom.

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.

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