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Complete set of bound negative-parity states in the neutron-rich nucleus N-18

2021    Ziliani, S.; Ciemala, M.; Crespi, F. C. L.; Leoni, S.; Fornal, B.; Suzuki, T.; Otsuka, T.; Maj, A.; Bednarczyk, P.; Benzoni, G.; Bracco, A.; Boiano, C.; Bottoni, S.; Brambilla, S.; Bast, M.; Beckers, M.; Braunroth, T.; Camera, F.; Cieplicka-Orynczak, N.; Clement, E.; Clement, E.

High-resolution. -ray spectroscopy of N-18 is performed with the Advanced GAmma Tracking Array, following deep-inelastic processes induced by an O-18 beam on a Ta-181 target. Six states are newly identified, which together with the three known excitations exhaust all negative-parity excited states expected in N-18 below the neutron threshold. Spin and parities are proposed for all located states on the basis of decay branchings and comparison with large-scale shell-model calculations performed in the p-sd space, with the YSOX interaction. Of particular interest is the location of the 0(1)(-) and 1(2)(-) excitations, which provide strong constrains for cross-shell p-sd matrix elements based on realistic interactions and help to simultaneously reproduce the ground and first-excited states in N-16 and N-18, for the first time. Understanding the N-18 structure may also have significant impact on neutron-capture cross-section calculations in r-process modeling including light neutron-rich nuclei.