How did Deuterium form?

  1. Hi,
    quite new in chemistry..
    I would like to know the beginning of the atoms in the universe.
    Therefore I must understand the process from Hydrogen to Helium. But
    to create Helium you need the isotope(#2) "Deuterium" from Hydrogen.

    But how did the Deuterium form? From two Protons colliding or did two Protium
    (also an isotope, #1)-atoms became a pair? If it became a pair, how could they
    resist the repelling force between them?
     
  2. jcsd
  3. Drakkith

    Staff: Mentor

    In the early universe the energy of the particles was high enough for protons to fuse together. During this process, two protons come together and one undergoes beta decay, turning into a neutron so that there is no longer any repulsion. See the following article. (It's about the p-p chain inside stars, but it's the same process in the early universe)

    http://en.wikipedia.org/wiki/Proton–proton_chain_reaction
     
  4. Protons do not decay, except in some "beyond the standard model" theories that have no experimental support behind them!

    After the big bang, there was both protons and neutrons in the early universe. Some of the nucleons formed deuterium, but most of this deuterium went into the formation of 4He. The left-over deuterium is what we observe in the present universe.
     
  5. Drakkith

    Staff: Mentor

    Ah, I had forgotten about the neutrons that were present. However, protons do in fact undergo beta decay during proton-proton fusion. (Specifically beta-plus decay)

    Edit: Note that this beta decay only happens when the protons fuse together. Lone protons do not decay.
     
    Last edited: Nov 13, 2013
  6. DrDu

    DrDu 4,090
    Science Advisor

  7. Thanks for your help ,

    If I also might ask:

    Did the decay have anything to do with the process
    of creating the first atoms, or, did it happen after?
    And,
    which came first, Alfa-decay or Beta-decay? Alfa decay is from what
    I've understand only for helium-nucleus.
     
  8. Drakkith

    Staff: Mentor

    Only slightly. Most of the deuterium was created by free neutrons fusing with protons, and only a small amount was from proton-proton fusion. I was a little mistaken on my first post, as I forgot about the free neutrons and the very short timescale that big bang nucleosynthesis took place in.

    I'm not sure you can really classify them as one coming before the other. Alpha decay is defined as the ejection of a helium nucleus from an atom, while beta decay is when an atom emits a beta particle (electron or positron) from its nucleus. I guess that if you go off the timeline, beta decay would come first, as practically no atoms were formed that underwent alpha decay during BBN.
     
  9. Ok then I understand :smile:
    Thx again.
     
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