Two neutron decay of 16Be
Recently, the first example of two-neutron decay from the ground state of an unbound nucleus, 16 Be, was seen (A. Spyrou, et. al ., Phys. Rev. Lett. 108 102501 (2012)). 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 under-bound by approximately 0.7 MeV with a width of approximately 0.17 MeV. For such a system, an attractive three-body force must be included to reproduce the experimental ground state energy.