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Natural Fission

  1. Feb 18, 2017 #1
    If the sun and cosmic objects are powered by nuclear fusion.. why is there fission in nature via Uranium or Plutonium.. what purpose does it serve for nature since nature doesn't use it.

    Unless there are natural processes that uses fission or heat from slow fission (maybe heating up the earth)? What actual processes?
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  3. Feb 18, 2017 #2


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    This process is estimated to be responsible for approx. half of the internal heat budget of Earth.

    Why would any natural process need a purpose? It exists whether or not we can assign to it something that we may deem 'useful'. What's the purpose of neutrinos? Of antimatter? Of rainbows?
  4. Feb 18, 2017 #3


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    Under certain conditions, light elements fuse into heavier elements in stars. There various possibilities, but the two main processes are the pp-chain and CNO-cycle.


    The production of heavy elements occurs in massive stars in what are called the r-process and s-process.

    So, all the elements on the earth started in stars, if not the 'Big Bang'.

    For every element, there are isotopes. One can find charts of the nuclides, which show the elements and their isotopes, some of which are stable, and most which are not.

    Radionuclides decay, and the ones we find on the earth or in nature have long half-lives, hence they can be formed millions or a few billion years ago, and some are still around. The transuranic radionuclides decay fairly rapidly, including undergoing spontaneous fission, so they are not abundant in nature.

    Fission can happen in nature, but under certain special conditions.
  5. Feb 19, 2017 #4
    Thanks.. just would like to know the following and don't want a separate thread.

    The sun nuclear fusion doesn't use deuterium and tritium right?

    Say we can somehow separate the hydrogen from water and find a way to compress the hydrogen directly.. they can form nuclear fusion?
  6. Feb 19, 2017 #5
    Separating hydrogen from water is easy.
    Compressing hydrogen is more difficult but can be done.
    As far as I know about the fusion process in the Sun, it does involve all isotopes of hydrogen,
    not just the vanilla form of it without neutrons
  7. Feb 19, 2017 #6


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    Deuterium is an intermediate product from p + p => d + e+ + v,
    then p + d => He3 + γ

    There may be the odd d+d or d+t fusion reactions, but these would be incidental and very infrequent (or be of low probability).

    We wouldn't be able to compress hydrogen to the pressures and densities necessary, and the pp-cycle has fairly low power density, even with the high densities in the sun.
  8. Feb 20, 2017 #7
    So in the sun, what is the percentage of fusion that involves the ordinary Hydrogen atoms that you can buy easily on earth?
  9. Feb 20, 2017 #8
    Astronuc makes it clear that nearly all of it is ordinary hydrogen, although d + t can contribute a small amount.
    The much greater abundance of ordinary hydrogen in the Sun simply makes it much more likely that ordinary hydrogen nuclei will be the ones fusing
  10. Feb 20, 2017 #9
    So theoretically.. if we extract all hydrogen in the water in the ocean and send the hydrogen to the sun core, it can form nuclear fusion there right due to having enough pressure and gravity for the fusion to occur. I just want to know if the hydrogen in water is exactly the same as the hydrogen the sun used for nuclear fusion.
  11. Feb 20, 2017 #10
    What does it mean "pp-cycle has fairly low power density, even with the high densities in the sun".. did you mean pp-cycle has low density in nature or on earth labs or do you mean pp-cycle has low power density in the sun.. yet you mentioned "even with the high densities in the sun". I'm confused with your language. Kindly rephrase it. Thanks.
  12. Feb 20, 2017 #11
    Yes it's exactly the same, both the Sun and ordinary water contain normal hydrogen predominantly
  13. Feb 20, 2017 #12


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    It means, that per unit volume, fusion in the solar core produces roughly as much power as a compost heap (~280W/m3). It just happens to be a rather large compost heap.
  14. Feb 20, 2017 #13
    So how many pieces of hydrogen can be used to create explosion the size of Hiroshima? How do you compute for it? Note let's ignore the fission stage where it proves the temperature and pressure for fusion to occur. Let's assume we are putting it in the core of the sun where gravity and pressure provides the environment for fusion.

    Just for comparison. If we take all the hydrogen of all water on earth and send it to the sun. How big the fusion explosion and how long? just want an idea (won't try to do it).
  15. Feb 20, 2017 #14
    The WW2 bombs were fission bombs, fusion bombs were tested later but not used in any war.
    A fusion bomb can develop a lot more explosive power, and they make use of a fission bomb just as a detonator.
    I think the Soviets tested one bomb which used a fission bomb to detonate a hydrogen bomb, but that bomb was itself just a detonator of an even bigger hydrogen bomb.

    On your other point, dumping a load of hydrogen onto the Sun produced from Earths sea water would make very little difference to it.
    The Sun is nearly all hydrogen anyway, (though fusion is happening only in the core).
    All the hydrogen on Earth, would increase the total amount of hydrogen in the Sun by a lot less than 1%
  16. Feb 20, 2017 #15
    If all the hydrogen on earth ocean were put in the core of the sun and they are part of the nuclear fusion.. how big would be the explosion.. how many TNT equivalent? or for comparison.. how many TNT equivalent that can destroy what size of country or would it (the TNT equivalent) like destroy 1/4 of the earth? Please actually compute. Thanks.
  17. Feb 20, 2017 #16


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    The proton-proton version of fusion that dominates in the Sun is far slower than that which occurs with the heavier nuclei used in weapons or would be used in future terrestrial fusion reactors. IIRC, the power density of P-P fusion in the Sun's core is about that of toaster oven per cubic meter. The half-life of a proton in the Sun's core is a billion years before it fusions (wiki). By contrast, the hydrogen isotope deuterium (fusion reactors, weapons) has a fusion life of 4 seconds on the Sun. It must be that way, else the Sun would have burned hotly through its fuel long ago. So P-P fusion is not very explosive on per cubic meter basis, though with 1027 cubic meters, P-P power density makes for a comfy star lasting billions of years.
  18. Feb 20, 2017 #17
    Ok. Thanks. That makes sense now.

    About nuclear weapons.. how many times can they produce this cycle of fission to fusion.. then the energy of fusion to produce more neutrons for more fission (in the casing) and more fusion and fission.. and so on. Is there a limit to the size?

    Is there a limit to the explosive power of a nuclear bomb? 50,000 years from now. Can they make a nuclear bomb that can detonate say the entire moon?
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