LK13350 - 26O, consisting of 8 protons and 18 neutrons has been predicted to beta-decay to 26F, however, extensive searches have found no
evidence for the existence of 26O nor for this decay mode. In this paper we demonstrated for the first time that 26O after it is formed breaks up into two neutrons and 24O. The data suggest that the neutrons are emitted simultaneously,
possibly as a di-neutron, an exotic decay mode which was discovered only a month ago in the decay of 16Be. The measured mass of 26O is a critical milestone towards the understanding of the question why oxygen can bind only 14 neutrons
(24O) while fluorine with only one additional proton can bind at least six more neutrons (31F has 22 neutrons and 9 protons).
