Abstract
Halo nuclei are formed when the last protons or neutrons are weakly bound to a tightly bound core. This allows the halo nucleons to tunnel far away from the core, resulting in a large r.m.s radius and therefore a large reaction cross section. Usually, halo nuclei possess only one bound state, the ground state, with all excited states being more or less unbound. When a nuclear potential is too weak to form a bound ground or excited state, the state can nevertheless be manifest physically as a positive energy resonance. Experimentally, low energy resonance like structures have been observed in the three-body continuum of certain halo nuclei eg. 6He → alpha + n + n. However, from a strict theoretical point of view, a resonance corresponds to a pole in the scattering amplitude at a complex energy. Halo nuclei have been successfully modelled as three-body systems in the hyper-spherical harmonic calculation scheme. Here the R-matrix method is used in solving the coupled hyperradial equations. It is critical that the long-range nature of the couplings in this system are incorporated correctly when evaluating the S-matrix. This is achieved through the use of coupled asymptotic solutions to the radial equation. These procedures have enabled a number of resonance-like S-matrix poles to be located for the 2+, 0+ and 1- spin-parity states in the low energy continuum of 6He.