A search for the neutron-unbound nucleus 21 C was performed via the single proton removal reaction from a beam of 22 N at 68 MeV/u. Neutrons were detected with the Modular Neutron Array (MoNA) in coincidence with 20 C fragments. No evidence for a low-lying state was found, and the reconstructed 20 C+n decay energy spectrum could be described with an s-wave line shape with a scattering length limit of |a s | < 2.8 fm, consistent with shell model predictions. A comparison with a renormalized zero-range three-body model suggests that 22 C is bound by less than 70 keV.
The technique of invariant mass spectroscopy has been used to measure, for the first time, the ground state energy of neutron-unbound 28 F, determined to be a resonance in the 27 F + n continuum at 220(50) keV. States in 28 F were populated by the reactions of a 62 MeV/u 29 Ne beam impinging on a 288 mg/cm 2 beryllium target. The measured 28 F ground state energy is in good agreement with USDA/USDB shell model predictions, indicating that p f shell intruder configurations play only a small role in the ground state structure of 28 F and establishing a low-Z boundary of the island of inversion for N = 19 isotones.PACS numbers: 21.10.Dr, 21.10.Pc A hallmark of the nuclear shell model is its reproduction of large energy gaps at nucleon numbers 2, 8, 20, 28, 50, 82, and 126. Although well established in stable nuclei, these magic numbers begin to disappear for nuclei far from stability. For example, it has been known for over 30 years that the large shell gap at N = 20 diminishes for neutron-rich nuclei [1][2][3][4]. The change in shell structure around N = 20 is now known to be a result of the tensor force, which is strongly attractive for the spin flip pairs πd 5/2 -νd 3/2 and strongly repulsive for the pairs πd 5/2 -ν f 7/2 [5][6][7]. For nuclei in the region of N ∼ 20 and Z 13, the reduced N = 20 gap allows p f shell intruder configurations, in the form of multi-particle, multi-hole (npnh or nℏω) cross shell excitations, to compete with standard sd only configurations if the gain in correlation energy is on the same order as the size of the shell gap [8][9][10]. This has led to the establishment of the "island of inversion"-a region of nuclei near N = 20 for which the intruder configuration is dominant in the ground state.
No abstract
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.