Dineutron

Dineutron (nn)
properties
electric charge	neutral
Spin parity	0 +
Isospin	1 (z component −1)
average lifespan	(not bound)

The dineutron is a particle made up of two neutrons . It was first observed in 2012 in the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University during the decay of the artificial neutron-rich isotope ¹⁶ Be (12 neutrons instead of 5 as in the stable isotope). The resulting dineutron was very short-lived. Like the diproton, the dineutron itself is not bound, albeit close to the limit of stability. As with the diproton, the explanation for this is to be found in a combination of the Pauli principle (with the result that the neutrons form a singlet with antiparallel spins) and the spin-dependency of the nuclear force (stronger when the nucleons spin parallel).

Attempts had already been made in other neutron-rich nuclei such as helium-10 and hydrogen-5 to observe decays with the emission of dineutrons, but the emission of single neutrons was preferred there. In the case of beryllium-16, however, the intermediate nucleus created when a single neutron is emitted would be even more unstable than the starting nucleus. Evidence that the neutrons - as predicted by the theory - in neutron-rich nuclei with an even neutron number such as helium-6 and -8 form pairs ( pairing in the form of Cooper pairs ) existed before.

In the series of neutron clusters , the Dineutron is the smallest representative. The only known bound state in this series is the neutron star . In contrast to the Dineutron, it is not the nuclear force but gravity that is responsible for the bond. There is also controversial experimental evidence of a bound tetraneutron .

Individual evidence

1. ↑ Artemis Spyrou et al. a .: First Observation of Ground State Dineutron Decay: ¹⁶ Be . In: Physical Review Letters , Volume 108, 2012, p. 102501
2. ↑ Michael Schirber: Focus: Nuclei Emit Paired-up Neutrons , APS Physics, March 9, 2012