Neutron-unbound states in Ne31
| Autor: | T. Mix, K. Stiefel, H. Karrick, B. Monteagudo, Anthony Kuchera, H. Liu, Nathan Frank, D. Votaw, Paul DeYoung, J. A. Brown, W. F. Rogers, A. Spyrou, J. McDonaugh, Michael Thoennessen, Thomas Baumann, D. Chrisman, C. Cochran, Thomas Redpath, Joseph E. Finck, R. Seaton-Todd, A. Blake, Paul Gueye, J. A. Tostevin, B. A. Brown |
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| Rok vydání: | 2021 |
| Předmět: | |
| Zdroj: | Physical Review C. 104 |
| ISSN: | 2469-9993 2469-9985 |
| Popis: | Background: The island of inversion near the $N=20$ shell gap is home to nuclei with reordered single-particle energy levels compared with the spherical shell model. Studies of $^{31}\mathrm{Ne}$ have revealed that its ground state has a halo component characterized by a valence neutron orbiting a deformed $^{30}\mathrm{Ne}$ core. This lightly bound nucleus with a separation energy of only ${S}_{n}=170$ keV is expected to have excited states that are neutron unbound.Purpose: The purpose of this experiment was to investigate the low-lying excited states in $^{31}\mathrm{Ne}$ that decay by the emission of a single neutron.Methods: An 89 MeV/nucleon $^{33}\mathrm{Mg}$ beam impinged on a segmented Be reaction target. Neutron-unbound states in $^{31}\mathrm{Ne}$ were populated via a two-proton knockout reaction. The $^{30}\mathrm{Ne}$ fragment and associated neutron from the decay of $^{31}\mathrm{Ne}$ were detected by the MoNA-LISA-Sweeper experimental setup at the National Superconducting Cyclotron Laboratory. Invariant-mass spectroscopy was used to reconstruct the two-body decay energy ($^{30}\mathrm{Ne}+n$).Results: The two-body decay energy spectrum exhibits two features: a low-lying peak at $0.30\ifmmode\pm\else\textpm\fi{}0.17$ MeV and a broad enhancement at $1.50\ifmmode\pm\else\textpm\fi{}0.33$ MeV, each fit with an energy-dependent asymmetric Breit-Wigner lineshape representing a resonance in the continuum. Accompanying shell-model calculations using the FSU interaction within NuShellX, combined with cross-section calculations using the eikonal reaction theory, indicate that these peaks in the decay energy spectrum are caused by multiple resonant states in $^{31}\mathrm{Ne}$.Conclusions: Excited states in $^{31}\mathrm{Ne}$ were observed for the first time. Transitions from calculated shell-model final states in $^{31}\mathrm{Ne}$ to bound states in $^{30}\mathrm{Ne}$ are in good agreement with the measured decay energy spectrum. Cross-section calculations for the two-proton knockout populating $^{31}\mathrm{Ne}$ states as well as spectroscopic factors pertaining to the decay of $^{31}\mathrm{Ne}$ into $^{30}\mathrm{Ne}$ are used to examine the results within the context of the shell-model expectations. |
| Databáze: | OpenAIRE |
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