  The complex-rotated hyperspherical adiabatic method is used to study the
decay of low-lying $^9$Be resonances into one neutron and two
$\alpha$-particles. We investigate the six resonances above the break-up
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 $^8$Be and $^5$He two-body
substructures are determined. We compute the branching ratio for sequential
decay via the $^8$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.

Nuclear Theory