Structure of 10He Low-Lying States Uncovered by Correlations

The 0(+) ground state of the He-10 nucleus produced in the H-3(He-8, p)He-10 reaction was found at about 2.1 +/- 0.2 MeV (Gamma similar to 2 MeV) above the three-body He-8 + n + n breakup threshold. Angular correlations observed for He-10 decay products show prominent interference patterns allowing us to draw conclusions about the structure of low-energy excited states. We interpret the observed correlations as a coherent superposition of a broad 1(-) state having a maximum at energy 4-6 MeV and a 2(+) state above 6 MeV, setting both on top of the 0(+) state tail.'' This anomalous level ordering indicates that the breakdown of the N = 8 shell known in Be-12 thus extends also to the He-10 system.