The structure and decay of ${}^{26}\mathrm{O}$ are investigated in a three-body ${}^{24}\mathrm{O}+n+n$ model suitable for studies of the long-lived (including radioactivity time scale) states. We have found extremely strong effects of the subbarrier configuration mixing on the decay width of true $2n$ emitters due to core recoil and neutron-neutron final state interaction. This effect far exceeds the analogous effect in the true $2p$ emitters. Our calculations provide reasonably narrow boundaries for the lifetime vs decay energy dependence for the true $2n$ emission. An upper limit of $\sim 1\mathrm{keV}$ for the decay energy of the unbound ${}^{26}\mathrm{O}$ is inferred based on the recent experimental lifetime value.

• Received 16 April 2013

DOI:https://doi.org/10.1103/PhysRevLett.111.042501