Talk:Dineutron
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[edit] puzzle
The article states:
- A system made up of only two neutrons is not bound, though the attraction between them is very nearly enough to make them so.
That is hard to accept, if two other facts are combined.
- Diprotons are unstable because the electrostatic repulsion of the two protons' positive charges overcomes the strong nuclear force holding them together. If the strength of the strong force had been only 2% greater, all protons would bind together into stable diprotons.
- The nuclear force is nearly independent of whether the nucleons are neutrons or protons.
Thus the (attractive) nuclear force between the neutrons in a dineutron should be about a large as the (repulsive) electrostatic force between protons in a diproton. The dineutron should be strongly bound (albeit unstable). Clearly there is a crucial piece of information missing here.
—Herbee 21:11, 6 July 2006 (UTC)
Oh wait, I found some more pieces of the puzzle.
- The deuteron has a spin of +1 (not zero as I would naïvely expect).
- The nuclear force depends on whether the spins of the nucleons are parallel or antiparallel.
So (I'm guessing here!) possibly the nuclear force is only attractive if the nucleons in a dinucleon have parallel spins, which the Pauli exclusion principle forbids. Please confirm or ridicule.
—Herbee 21:47, 6 July 2006 (UTC)
- Seconded Rod57 03:31, 9 November 2007 (UTC)
Incase it helps - CERN Ask an Expert Service responded : "The deuteron (one proton plus one neutron) has angular momentum (spin) of one unit. The proton and neutron are in a state of zero orbital angular momentum with their spins (of 1/2) aligned. If we replaced the proton by another neutron, we would have two identical fermions (neutrons) in exactly the same state. This is not allowed by the 'Pauli exclusion principle'." > Question: Since proton and neutron form stable deuteron, Why dont 2 > neutrons bind with the strong nuclear force ?
Just found a similar explanation on deuteron#Nuclear properties "...the corresponding spin-1 state does not exist in the two-neutron or two-proton system, due to the Pauli exclusion principle which would require one or the other identical particle with the same spin to have some other different quantum number, such as orbital angular momentum. But orbital angular momentum of either particle gives a lower binding energy for the system, primarily due to increasing distance of the particles in the steep gradient of the nuclear force. In both cases, this causes the di-proton and di-neutron nucleus to be unstable."
However Semi-empirical_mass_formula#Pairing_term says "in the shell model, two protons with the same quantum numbers (other than spin) will have completely overlapping wavefunctions and will thus have greater strong interaction between them and stronger binding energy. This makes it energetically favourable (i.e. having lower energy) for protons to pair in pairs of opposite spin. The same is true for neutrons."
The final part of the sentence "A system made up of only two neutrons is not bound, though the attraction between them is very nearly enough to make them so." perhaps needs clarifying. Rod57 (talk) 21:28, 22 May 2008 (UTC)
