Low-lying level structure of the neutron-unbound $\textit{N}$ = 7 isotones

This article reports on results of an experimental search for ground state shell inversion in the neutron-unbound $\textit{N}$ = 7 isotones 9He and 10Li. Two different radioactive ion beams (11Be, Elab = 44 MeV/u and 12B, Elab = 45 MeV/u) impinging on a beryllium target were used to directly and selectively populate unbound states of a given ℓ in the nuclides of interest. Be(11Be, 8He + $\textit{n}$) and Be(12B, 8He + $\textit{n}$) reactions populated unbound states in 9He. Fragments and neutrons were detected in coincidence to reconstruct the decay energy of 9He using invariant mass spectroscopy. Similarly, Be(11Be, 9Li + $\textit{n}$) and Be(12B, 9Li + $\textit{n}$) reactions were used to populate unbound states in 10Li, and the time-of-flight method was used to determine the relative velocity of the 9Li fragments and neutrons in coincidence. Various states in both 9He and 10Li were observed and characterized. Here, the data indicate possible ground state shell inversion in both cases.