Structure of pairs in heavy weakly-bound nuclei

We study the structure of nucleon pairs within a simple model consisting of a square well in three dimensions and a delta-function residual interaction between two weakly-bound particles at the Fermi surface. We include the continuum by enclosing the entire system in a large spherical box. To a good approximation, the continuum can be replaced by a small set of optimally-determined resonance states, suggesting that in many nuclei far from stability it may be possible to incorporate continuum effects within traditional shell-model based approximations.