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My question is why aren't we seeing 4 neutrons sticking together

  1. Jul 9, 2003 #1
    We all know that the helium nucleus is very stable because it consists of two protons and two neutrons.
    My question is why aren't we seeing 4 neutrons sticking together forming an even more stable nuclide, since neutrons exert only the strong attractive nuclear force but not the repulsive Coulomb force?
     
    Last edited by a moderator: Feb 5, 2013
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  3. Jul 9, 2003 #2

    HallsofIvy

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    It's not that neutrons don't stick together but that they don't form nuclides- you have to have at least one proton to have a nuclide: no protons, no electrons and so no atom! It is, after all, the electrons that give atoms their chemical identity.
     
  4. Jul 9, 2003 #3
    You do get clumps of nuetrons though.
    Isn't that what a nuetron star is supposed to be?
     
  5. Jul 9, 2003 #4

    Janus

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    Left by themselves, neutrons are unstable, with a half-life of 12 mins, and decay into a proton and electron.

    The presence of already existing protons curtails this. When you have the right porportion, you get a stable nucleus. Otherwise, a nucleus with too many neutrons tends to undergo beta- decay (a neutron change to a proton and emits an electron.)

    Nuclei with too few neutrons are unstable also, due to the fact that there aren't enough neutrons to overcome the electrostatic repulsion of the protons.

    Neutron stars are stable because of the immense gravity due to their large mass. This squeezes the neutrons together so tightly that there isn't any "room" for the electrons which must be emitted in order for the neutrons to decay. (gravity overcomes the weak force)
     
  6. Jul 11, 2003 #5
    neutrons

    Thanks for the fast response!
    What I really want to find out is:

    In their natural occurring way, why don't neutrons seek out one another and form stable clumps? Bear in mind that 2 neutrons and two protons do just that and form a very stable helium nuclide, although there is quite a bit of repulsive force between the two protons.

    Could this have something to do with their quantum states being exclusive?
     
  7. Jul 11, 2003 #6
    Re: neutrons

    As Janus pointed out, they are unstable on their own, hence it could be assumed that that unstability precludes stable particulate formation.

    The manner of formation of the helium nucleous might be something you want to investigate, first.
     
  8. Jul 11, 2003 #7

    Janus

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    Re: neutrons

    Again, neutrons are unstable. If such a clump were to form, the neutrons would start to decay until enough protons were formed to create a stable nucleus.

    It is the electrostatic repulsion of the protons with each other that would stop the process. After a certain point, the combined replusion of the protons overrides the weak interaction that causes neutron decay, preventing the formation of any more protons.
     
  9. Jul 11, 2003 #8

    selfAdjoint

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    The nuclei are held together by the constant exchange of particles (pions, or if you prefer, quarks) which cause the protons and neutrons to change into each other. Two protons by themselves can't support that, and neither can two neutrons. So you don't see all proton or all neutron nuclei. Except for Hydrogen of course, a single proton all by its lonesome.
     
  10. Jul 11, 2003 #9
    Do you have a reference for that statement? (the one in red)
     
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