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Why in hydrogen fusion are neutrinos ejected?

  1. Mar 16, 2009 #1
    Hi, I was wondering:

    why in hydrogen fusion are neutrinos ejected?

    why in fission does the neutron actually knock over neutrons out of atoms

    the nucleon are held together in the nuceus by nuclear forces which over power electrostatic forces. But what actually generates these forces? Are electrons not in the nuclear because of their size and mass exerts little nuclear force?

    Thanks :)
     
  2. jcsd
  3. Mar 16, 2009 #2

    malawi_glenn

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    Re: Fission/Fusion

    i) do preserve lepton number conservation, the neutrino emitted is an electron-neutrino, which carries no electric charge and electron lepton number +1. Emitted is also a positron, which carries electric charge +1 and electron lepton number -1. The protons (hydrogen nucleus) has no lepton number at all.

    ii) are you referring to neutron induced fission? I can't even make up a correct sentence out of what you wrote.

    http://library.thinkquest.org/17940/texts/fission/fission.html

    The nucleus will be split into two halves and some free neutrons, the final result is probabilistic and the result will occur since it can occur (is more energetically favourable)

    http://www.knutsford-scibar.co.uk/webimages/fission.jpg [Broken]

    iii) I think you are asking what is the attractive force that helds nucleons together, and that is the strong nuclear force:

    http://en.wikipedia.org/wiki/Nuclear_force

    http://aether.lbl.gov/elements/stellar/strong/strong.html

    the concept is that only protons have EM-force, which is repulsive and infinite range, but quite weak in strength. Both protons and neutrons have attractive force called the nuclear force, which is strong but short ranged - only nearby neighbour nucleons feel that force.

    Now look at the image on fission again, the incoming neutron will disturb the mother nucleus and make it elongated. The ratio of neighbours will decrease at the middle where it is thin, thus the electromagnetic force might take over and force the elongated nucleus to split in two + some neutrons. The yeild of daughter nuclei follows a distribution, here are some examples:

    http://www.kayelaby.npl.co.uk/atomic_and_nuclear_physics/4_7/4_7_1a.html

    also the number of neutrons in the final state also vary, from 0 to quite many, like 6-8. The mean is around 4, depending on what mother nucleus you have and energy of incoming neutron.

    electrons will undergo reactions with the protons in the nucleus when they are 'inside' the nucleus, this is called electron capture http://en.wikipedia.org/wiki/Electron_capture
     
    Last edited by a moderator: May 4, 2017
  4. Mar 18, 2009 #3
    Re: Fission/Fusion

    Thank you very much.

    One query I have at current, according to
    http://aether.lbl.gov/elements/stellar/strong/strong.html

    mesons are what hold the nucleons together/reason of the strong nuclear force, yet mesons are not force carriers

    Isn't this because they decay in glueons which are the force carriers of strong nuclear force? I've been googling and without my luck, which is strange. Do you knwo the full story of mesons to glueons?

    Thanks :)
     
  5. Mar 18, 2009 #4

    malawi_glenn

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    Re: Fission/Fusion

    Why are they NOT force carriers? It is easy to construct a theory of hadron interactions where they are the bosons responsible for interactions (see Chiral Perturbation Theory for instance, and meson exchange potential)

    The thing is that at hadronic energy scales, QCD is not asymptotic free, so it is hard/meaningless to speak about quarks and gluons, what exists are hadrons; Mesons and Baryons.

    Easy lectures:
    http://arxiv.org/PS_cache/hep-ph/pdf/9501/9501357v1.pdf
    http://en.wikipedia.org/wiki/Nuclear_force


    Advanced lectures:
    http://arxiv.org/PS_cache/hep-ph/pdf/0210/0210398v1.pdf
    http://arxiv.org/PS_cache/hep-ph/pdf/9501/9501357v1.pdf


    It is a difference between the strong force (quarks and gluons) and the strong nuclear force (hadrons)

    Mesons do NOT decay into gluons....

    By the way, it is difficult to understand what you are saying sometimes, I guess English is not your native languange?
     
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