Neutron Stabilization mechanism?

  1. May 14, 2014 #1
    If a neutron is unstable outside the nucleus, then what makes it stable within the nucleus? Does the binding of particles together somehow make them stable?

    Neutrons decay via the weak force, but are bound in the nucleus by the strong force. Does the strong force inhibit the weak force?

    Are muonium and tauonium more stable than muons and tau particles, respectively?
     
  2. jcsd
  3. May 14, 2014 #2

    Bill_K

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    An isolated neutron decays to a proton because the decay is energetically possible - the neutron has more mass energy than the proton.

    To ask whether the decay of a neutron within a nucleus is energetically possible, you have to compare the total mass energy of the original nucleus to that of the daughter nucleus having one more proton and one fewer neutron. Sometimes this is not favorable. Sometimes it is, in which case the nucleus undergoes beta decay, emitting an electron and an antineutrino.
     
  4. May 17, 2014 #3
    Some times in a nucleus you will have protons reverse beta decay into neutrons. That will happen when that reverse reaction is the one that is energetically favorable. It all depends on whether the reaction is exothermic which can happen spontaneously or whether it is endothermic in which case an external energy source is required.
     
  5. May 18, 2014 #4
    So, how does the individual neutron "know" about the rest of the nucleus, as far as how many protons and neutrons it has?
     
  6. May 18, 2014 #5

    Bill_K

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    Think of it as a decay of the entire nucleus. There's no way to identify which neutron decayed. All the particles in the nucleus are constantly exchanging energy with each other.
     
  7. May 18, 2014 #6

    mfb

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    You can ask the same question on a deeper level, as it is possible to describe beta decay as "down-quark goes to up-quark plus electron plus antineutrino". How does the down-quark in a free proton "know" that it cannot decay? Bill_K gave the answer: it is a decay of the whole bound system.

    Those are just bound by the electromagnetic interaction, it is not strong enough to influence the decays in any relevant way. "True muonium" (##\mu^+ \mu^-##) is different, it would almost always annihilate long before the muons decay.
     
    Last edited: May 18, 2014
  8. May 18, 2014 #7
    The same way a photon knows when there are two open slits in the double slit experiment.
     
  9. May 19, 2014 #8
    Standing alone, you would fall if you relax and stop maintaining your balance. But if locked into a 0.5x0.5 room, you can't fall.

    Nucleaus is a "room" for the neutron.
     
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