The neutron-unbound nucleus 15Be was observed for the first time. It was populated using neutron transfer from a deuterated polyethylene target with a 59 MeV/u 14Be beam. Neutrons were measured in coincidence with outgoing 14Be particles and the reconstructed decay energy spectrum exhibits a resonance at 1.8(1) MeV. This corresponds to 15Be being unbound by 0.45 MeV more than 16Be thus significantly hindering the sequential two-neutron decay of 16Be to 14Be through this state. The cross section for neutron pick up was calculated to be 1.1(6) mb, and 0.7(5) mb from carbon, and deuterium, respectively.
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