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The structure and decay of the most neutron-rich beryllium isotope, ^16Be, has been investigated following proton knockout from a high-energy ^17B beam. Two relatively narrow resonances were observed for the first time, with energies of 0. 84 (3) and 2. 15 (5) MeV above the two-neutron decay threshold and widths of 0. 32 (8) and 0. 95 (15) MeV, respectively. These were assigned to be the ground (J^π=0^+) and first excited (2^+) state, with Eₗ=1. 31 (6) MeV. The mass excess of ^16Be was thus deduced to be 56. 93 (13) MeV, some 0. 5 MeV more bound than the only previous measurement. Both states were observed to decay by direct two-neutron emission. Calculations incorporating the evolution of the wave function during the decay as a genuine three-body process reproduced the principal characteristics of the neutron-neutron energy spectra for both levels, indicating that the ground state exhibits a strong spatially compact dineutron component, while the 2^+ level presents a far more diffuse neutron-neutron distribution.
Monteagudo et al. (Fri,) studied this question.