Low-lying level structure of the neutron-unbound N=7 isotones (original) (raw)

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