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 $2^{ +}$, to the resonances at 0.89, 2.03, 5.13, respectively. The computed structures are in agreement with existing reaction measurements.
Categories: nucl-th