Recently, the first example of two-neutron decay from the ground state of an unbound nucleus, $^{ 16}$Be, was seen. Three-body methods are ideal for exactly treating the degrees of freedom important for these decays. Using a basis expansion over hyperspherical harmonics and the hyperspherical R-matrix method, we construct a realistic model of $^{ 16}$Be in order to investigate its decay mode and the role of the two-neutron interaction. The neutron-$^{ 14}$Be interaction is constrained using shell model predictions. We obtain a ground state for $^{ 16}$Be that is over-bound by approximately 1 MeV with a width of approximately 0.23 MeV. This suggests, that for such systems, the three-body force needs to be repulsive.
Categories: nucl-th