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What keep the nucleous from colapsing into its self

  1. Dec 17, 2006 #1
    I was just wonder what force keep protons from "merging" into eachother. As I understand, the reason I cant put my hand through a wall is due to the electromagnetic repulusion of electron. Protons on the other hand, repeal each other, but after a certian distance the strong nuclear force kicks in and they become attracted to eachothere?

    I guess my question can be rephrased why isn't baryonic matter allways an bose-enstien condestate.
  2. jcsd
  3. Dec 17, 2006 #2


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    I think it's due to the energy required to start that reaction. For example, hydrogen atoms can be joined to make helium atoms. This has been done many times before. The catch is that it requires extreme temperatures in the range of 800 million degrees Kelvin.

    Nuclear reactions are just like any other reactions. Enthalpy still strongly favours the burning of gasoline at -100C, yet gasoline cannot burn at -100C. Why? Not enough energy to start the reaction.

    edit: to sum up what I said, you need 800 million degrees Kelvin before the nuclei can get close enough for the strong nuclear force to overcome the coulomb force.
    Last edited: Dec 17, 2006
  4. Dec 17, 2006 #3
    Can I guess something? Could it have something to do with the uncertainy principle? Could it be that if the protons condensed into one big lump, the combination of momentum and location would be greater than Planck's constant? I have heard that proposed as an explaination for why electrons don't collapse onto the nucleus. Maybe the bose-enstien condestate can only occur because the momentum of the protons are so low near absolute zero.
  5. Dec 17, 2006 #4


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    I too would like to know the real answer for that. It just seems to make sense that eventually the nucleous would be slammed by an electron and the electron would never go away.
  6. Dec 18, 2006 #5
  7. Dec 18, 2006 #6
  8. Dec 23, 2006 #7
    Err, what do you mean about "the volume of space and it's location" ? Also, the model presented in the FAQ is THE ONLY correct model coming from QM, and it says JUST THE SAME (in another way) as the content of your reference.

    Last edited: Dec 23, 2006
  9. Dec 23, 2006 #8
    Haven't you answered your own question here. You already said Protons - "repel each other" so how could they merge into each other?
    You might guess that the Strong force should do it; but that only increases (to some limit) as distance increases not decreases like charge force. Or as you already put it "after a certain distance the strong nuclear force kicks in".

    I don't see where Bose-Einstein condensate would apply as that deals with electrons and nuclei working together. There the condensate is prevented until the kinetic energy contained in the movement we measure as temperature is removed.
  10. Dec 24, 2006 #9
    Ha, ha, Marlan, I see what you mean. Well, it is a good try for an engineer. At least I am not completely wrong.
  11. Dec 27, 2006 #10
    Don't worry, the content of the link you provided is entirely correct. I just wanted to point out that it is just the same as what i have been saying.

  12. Jan 27, 2007 #11
    Wrong question!

    The question is not why don't collapse protons into each other, since protons are same electrically charged, and strongly repell each other.

    So, the real question is: what keeps protons in the nucleus together?

    The answer is: the strong nuclear force. The individual parts of the proton, the quarks, bind together because they interact with gluons, the carrier of the strong nuclear force, and interchange bosons (W+/W-, Z).
  13. Jan 27, 2007 #12
    In the textbook(Introductory Nuclear Physics by Krane) I had in a nuclear physics class it says that the nucleon-nucleon interaction becomes repulsive at very small distances.

    When I read that I assumed the strong force itself becomes repulsive at short distances.
    But does it realy mean the columb repulsion dominate over the strong force at extremely small distances?
  14. Feb 7, 2007 #13
    Yes. The Strong force goes like exp(-ar)/r so it falls off very quickly when r is large, and the columb force (with it's 1/r^2 dependence) dominates when r goes to zero, So the strong force will only hold protons in place if they are close enough, and if they get too close, the columb repulsion takes over. i.e. it is in fact a stable equilibrium.
  15. Feb 8, 2007 #14

    But then there is the question of neutrons and what prevents them from "collapsing" into eachother or into protons.

    Do they come so close that the quark charges becomes significant?
  16. Mar 7, 2007 #15
    In short : conservation laws ! At the quark level, which indeed is the level we need to look at when studying the weak interaction, a neutron is NOT the same as a proton !

    But actually, you do not need to go THAT deep. I suggest you do some research. Try answering this question : what conservation laws need to be respected when a neutron decays into a proton and vice versa. Then you will understand why this decay does not happen "at random" in the nucleus.

    Last edited: Mar 7, 2007
  17. Mar 8, 2007 #16
    My wording was a bit poor. I did not question why neutrons doesnt decay into protons in stable nuclei. I was questioning why a neutron wont get "sucked" into a proton. If the nucleon-nucleon interaction is purely attractive why doesnt the neutron and proton get sucked into eachother. :confused:

    About the neutron decay I can offhand guess two things that prevent neutron decay in stable nuclei.

    One is the shell structure. If the proton shells are filled the proton after the decay would have to be put in a higher shell and this would probably make the decay impossible in most cases.

    In even-even nuclei maby the needed breaking of a pair could make the decay energeticly impossible.

    Are those guesses right??

    I cant figure out offhand what prevents decay of neutrons in nuclei with odd-odd or even-odd proton-neutron number.:confused: :confused:
  18. Mar 10, 2007 #17

    The fundamental interaction is not the strong interaction but the QCD (Quantum Chromodynamics ).
    The nucleon (proton or neutron) is not a point like particle. In fact there are three quark inside and a sea of virtual gluons. The interaction is very complicated. The Physical Review D54 Particle and Fields, at page 194 present the cross section data for a proton-neutron up to 500 Gev (center of mass).
  19. Mar 10, 2007 #18
    :confused: :confused: Care to elaborate why you think QCD and the strong interactions are not the same thing? How are you defining the "strong" interaction?
  20. Mar 10, 2007 #19
    You are right one must be careful.:rolleyes:
    I thought that you are talk about that (http://en.wikipedia.org/wiki/Nuclear_force) nuclear forces.
    (Not a fundamental one)
    I was talking about the QCD (http://en.wikipedia.org/wiki/Quantum_chromodynamics)
    where the interaction where the color charge is the origin of the interaction (http://en.wikipedia.org/wiki/Color_charge)
    The proton and the neutron have 0 total color charge. In fact all the mesons and all baryon have 0 color charge. The SU_color(3) group is responsible for that.
    In high energy (a lot of Gevs) there is asymptotic freedom and one can use perturbation theory (Feynman diagrams). In the low energy (500 Mev is realy low energy) one must use QCD latice using a super computer. This is very difficult and expensive.
    In energy region of the nuclear physics we treat the nucleons (protons and neutrons ) as point like particles with a Classical potential. In such low energy this is not a bad approximation.

    Now if one asked why one proton and one neutron they dont merge then he must use the full theory (no pertubative QCD).
    In fact if we use ultra high energy one can create quark gluon plasma (http://en.wikipedia.org/wiki/Quark-gluon_plasma.)

    1) I remember the decays of the Z0 during my Phd at CERN in the early 90s. When the Z0 decay to two quark we had two or three jet of particles.
    2) Sorry for this lengthy message, but I just discover your forum and I am really excited!:tongue2:
  21. Mar 10, 2007 #20
    Let me just add two comments.

    First, the quark and gluon plasma has not been observed unambigously. As of today, it is still a theoretical speculative possibility, not an established experimental fact.

    Second, one should not make such a difference between strong interaction and QCD. It is quite unusual to speak in those terms. In the field of strong interaction physics, everybody agrees that it is highly unlikely that QCD is not the correct and relevant model of strong interaction. Besides, were it at low (less than 100 MeV say) or high (more than 100 GeV say) energies one can actually make calculations using various perturbative technics (s.a., for instance, chiral perturbation theory at low energy, and direct application of Feynman's diagrams at high energy/momentum transfer). The real problem with non-perturbative QCD is in the intermediate energy range, not low energy. Even in the worse non-perturbative region for QCD, say between 100 Mev and a few GeVs, we do have at hand very convincing experimental facts establishing QCD as the correct model of strong interaction. And we are even able to perform some approximations and calculations, at 30% level. You would be extremly surprised by the efficiency of Regge-like (improved) calculations for instance in this regime, which rely merely on the most general properties of QFTs (causality, unitarity...).
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