[1] This has the consequence that if one component is removed, the remaining two comprise an unbound resonance, so that the original nucleus is split into three parts.
[4] Additionally, 9Be is a Borromean nucleus comprising two alpha particles and a neutron;[3] the removal of any one component would produce one of the unbound resonances 5He or 8Be.
Several Borromean nuclei such as 9Be and the Hoyle state (an excited resonance in 12C) play an important role in nuclear astrophysics.
Namely, these are three-body systems whose unbound components (formed from 4He) are intermediate steps in the triple-alpha process; this limits the rate of production of heavier elements, for three bodies must react nearly simultaneously.
These also lie along the drip lines; for instance, 8He and 14Be are five-body Borromean systems with a four-neutron halo.