 A two-neutron halo is exhibited by 6He, 11Li, 17B, 19B and 22C.Two-neutron halo nuclei break into three fragments, never two, and are called "Borromean nuclei" because of this behavior (referring to a system of three interlocked rings in which breaking any ring frees both of the others).8He and 14Be both exhibit a four-neutron halo.