section_path: Neutron compounds/Dineutrons and tetraneutrons
section_name: Dineutrons and tetraneutrons
paragraph_text: Dineutrons and tetraneutrons
  
  The dineutron is considered an unbound isotope with lifetimes around 10 seconds. The first evidence for this state was reported by Haddock et al. in 1965. In 2012, Artemis Spyrou from Michigan State University and coworkers reported that they observed, for the first time, direct dineutron emission in the decay of Be. The dineutron character is evidenced by a small emission angle between the two neutrons. The authors measured the two-neutron separation energy to be 1.35(10) MeV, in good agreement with shell model calculations, using standard interactions for this mass region.
  
  Evidence for unbound clusters of 4 neutrons, or tetraneutron as resonances in the disintegration of beryllium -14 nuclei, in He- Be interactions, and collisions of He nuclei give an estimated lifetime around 10 seconds. These discoveries should deepen our understanding of the nuclear forces.