We compute the three-body structure of the lowest resonances of ${}^{12}$Be considered as two neutrons around an inert ${}^{10}$Be core. This is an extension of the bound-state calculations of ${}^{12}$Be into the continuum spectrum. We investigate the lowest resonances of angular momenta and parities, $0^{\pm }$, $1^{-}$, and $2^{+}$. Surprisingly enough, they all are naturally occurring in the three-body model. We calculate bulk structure dominated by small-distance properties as well as decays determined by the asymptotic large-distance structure. Both $0^{+}$ and $2^{+}$ have two-body ${}^{10}$Be-neutron $d$-wave structure, while $1^{-}$ has an even mixture of $p$ and $d$ waves. The corresponding relative neutron-neutron partial waves are distributed among $s$, $p$, and $d$ waves. The branching ratios show different mixtures of one-neutron emission, three-body direct, and sequential decays. We argue for spin and parities $0^{+}$, $1^{-}$, and $2^{+}$ for the resonances at $0.89$, $2.03$, and $5.13$, respectively. The computed structures are in agreement with existing reaction measurements.

• Received 21 June 2012

DOI:https://doi.org/10.1103/PhysRevC.86.024310