Hypothetical nuclei

The tetraneutron is considered an unbound isotope with a lifetime around 10−22 seconds. The stability of this cluster of four neutrons is not supported by current models of nuclear forces. Recent empirical evidence is "consistent with a quasi-bound tetraneutron state existing for a very short time".

REDIRECT Isotopes of helium#Helium-2 (diproton)

REDIRECT Neutronium#In the periodic table