An atomic nucleus assumes discrete energy levels when added energy excites that nucleus. These energy levels are the unique nucleus fingerprint. No two nuclei have identical energy patterns. For exotic nuclei, which contain disproportionate numbers of protons and neutrons and are often only present for a fraction of a second, researchers have devised a variety of methods to measure the energies of their excited levels.
Researchers recently discovered unusual levels formed when a beam of calcium-38 traveling at 30 percent of the speed of light hit a beryllium-9 target. The Ca-38 nuclei lost a large amount of energy in the encounter.
The researchers traced the unusual excited levels formed in calcium-38 to the simultaneous excitation of many protons and neutrons. The energies of such complex states are sensitive investigations of nuclear theory. They are difficult to observe in interactions that are normally performed at high beam energies in particle accelerators.
Thus, these scattering-scattering interactions are a new tool in the arsenal of nuclear researchers who study and design nuclei. In the future, researchers could use these types of interactions to study the unusual energy levels in many other short-lived nuclei to explore the nuclear theory, for example, in the facility of rare isotope bundles.
Researchers have found a new pathway that leads to the formation of complex excited states in rare isotopes. They conducted the experiment at the National Superconducting Cyclotron Laboratory, a cyclotron-based particle accelerator at MSU that previously served as a user facility for the National Science Foundation. These excited states appear to involve rearrangements of several nucleons, formed in the collision of a single high-energy projectile target.
The energies of these states are sensitive parameters for model calculations of coincidences that span large model spaces. For the rare isotope calcium-38, the researchers observed enumerations of these energy levels by gamma-ray spectroscopy using Gretina.
This came after inelastic scattering in which the incoming calcium-38 beam interacted with a beryllium-9 target at more than 30 percent of the speed of light. The incoming bundle of calcium-38 has abruptly lost more than 200 MeV in energy. Such complex structure states have previously been elusive in fast beam experiments with high illumination usually without high energy loss. They often elude notice in low-energy interactions, which require much higher beam intensities.
This work was carried out in collaboration between experimentalists and theorists from Michigan State University, Washington University in St. Louis, Argonne National Laboratory, and the University of Surrey in the UK. Related research has been published in Physical review letters And physical review c.
Gade et al., Exchange interactions with mean energy bundles: a new approach to packing complex structure states into rare isotopes, Physical review letters (2022). DOI: 10.1103/PhysRevLett.129.242501
Gad et al. Exploiting scattering interactions to perform γ-beam spectroscopy of neutron-deficient isotopes Ca 38, 39, physical review c (2022). DOI: 10.1103/PhysRevC.106.064303
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