The complex-rotated hyperspherical adiabatic method is used to study the decay of low-lying ${}^9\mathrm{Be}$ resonances into one neutron and two $\alpha$ particles. We investigate the six resonances above the breakup threshold and below 6 MeV: $1/2^{\pm }$, $3/2^{\pm }$, and $5/2^{\pm }$. The short-distance properties of each resonance are studied, and the different angular momentum and parity configurations of the ${}^8\mathrm{Be}$ and ${}^5\mathrm{He}$ two-body substructures are determined. We compute the branching ratio for sequential decay via the ${}^8\mathrm{Be}$ ground state, which qualitatively is consistent with measurements. We extract the momentum distributions after decay directly into the three-body continuum from the large-distance asymptotic structures. The kinematically complete results are presented as Dalitz plots as well as projections on given neutron and $\alpha$ energy. The distributions are discussed and, in most cases, found to agree with available experimental data.

• Received 6 July 2010

DOI:https://doi.org/10.1103/PhysRevC.82.034001