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Why are only some particles fissionable/fissile?

  1. Nov 26, 2008 #1
    I understand how fission happens. But what I do not understand is why only a few certain nuclei are actually fissionable/fissile.

    Can anyone help?

    Thanks,
    Jamie
     
  2. jcsd
  3. Nov 26, 2008 #2

    mgb_phys

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  4. Nov 26, 2008 #3
    If more neutrons means a more stable nucleus, then why in nuclear fission does the absorbtion of an extra neutron lead to the nucleus splitting in half?
     
  5. Nov 26, 2008 #4

    mgb_phys

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    More neutrons only means more stable upto a certian level.
    There is a most stable ratio of neutrons/protons which gets slightly larger with larger atoms.
    So a small atom with an equal number of protons/neutrons would become very unstable if you added a single neutron. As you get larger the most stable configuration is a few more neutrons than protons - but if you add more neutrons than this you go off the line in the other direction and make the nucleus less stable.

    The exact number to have best stability can be calcuated but the theory (Quantum Chromo Dynamics) is very complicated.
     
    Last edited: Nov 27, 2008
  6. Nov 26, 2008 #5
    Okay, thanks very much.
     
  7. Nov 27, 2008 #6
    adding more neutrons results in a stronger force of attractin holding the neucleus together but it takes energy to produce neutrons which are themselves unstable. allowing a sungle neutron in such a nucleus to decay would cause the nucleus to expand but it also releases the energy stored in than nutron.

    uranium decays by a different process than most. it splits in half. the protons are in 2 shells which simply separate.
     
  8. Nov 27, 2008 #7

    Vanadium 50

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    No, it only does this if the nucleus is proton rich. Adding a neutron to a nucleus that is already neutron rich makes it worse.

    Yes, if I want a beam of neutrons it takes energy and they are unstable. But what does this have to do with the question.

    I don't think so.

    Alpha decay is common, and it's simply one example of spontaneous fission.
     
  9. Nov 27, 2008 #8
    the strong force increases when you add neotrons. but if you hove too many neutrons then the energy released by allowing a neutron to decay is greater than the decrease in energy due to the strong force.
     
  10. Nov 27, 2008 #9

    Vanadium 50

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    If your theory were true, Helium 5 would decay by beta emission, like a free neutron. In fact, it decays by simply falling apart to a neutron and an alpha.
     
  11. Nov 28, 2008 #10
    yes and a nucleus of 2 alpha particles will fall apart too. theres something inherently unltable about those configurations. dont know what that has to do with what I am saying though.
     
  12. Nov 28, 2008 #11

    Vanadium 50

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    It shows your theory is wrong. You said "the strong force increases when you add neotrons [sic]" until the neutron decays (via beta decay). Here's a situation where the nucleus becomes less stable and the neutron does not beta decay inside the nucleus.
     
  13. Nov 28, 2008 #12
    a single exception doesnt necessarily prove a rule wrong. its a big complex world with lots of exceptions.
     
  14. Nov 29, 2008 #13

    Vanadium 50

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    This is science. It matters when your theory gets something wrong. Especially when mainstream theory gets it right.
     
  15. Nov 29, 2008 #14

    malawi_glenn

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    granpa, the strong force is a saturating force. You are mixing wild between concept of force and binding energy.

    Uranium exihibit same fission spectra as the other heavy nuclei...


    Unredeemed: All nuclei are fissionable, but not everyone you can gain energy by splitting them.
     
  16. Nov 29, 2008 #15
    my 'theary' as you call it IS the mainstream view.
     
  17. Nov 29, 2008 #16

    malawi_glenn

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    "uranium decays by a different process than most. it splits in half. the protons are in 2 shells which simply separate. "

    Now first define WHAT uranium isotope you are referring to and state your source (peer reviewed article or textbook)
     
  18. Nov 29, 2008 #17
    ok I'll bite. what other heavy nuclei and what fission spectrum and what does any of that have to do with what I said?
     
  19. Nov 29, 2008 #18
    I was talking to malawi about the stability of lighter nuclei. please read the whole forum before you jump on people.
     
  20. Nov 29, 2008 #19

    malawi_glenn

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    I can't see where you state that: "For light nuclei...."

    Then you brought up the discussion about Uranium, therefor I asked what is so special about it and what isotope you are referring to. Don't you know what a fission spectra is?
     
  21. Nov 29, 2008 #20
    well I would assume you mean the different masses of the resulting nuclei but that doesnt seem to follow from what you said since I cant see any relevance to anything being discussed.
     
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