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How did we get elements above lead?

  1. Jun 4, 2009 #1
    This is something which has been a question to me that I don't seem to have stumbled across anything about myself:

    How and when did/do the elements above Iron get created?

    I've come across mention about the elements up to iron being generated by the process of fusion in stars. I assume you need bigger stars to fuse elements higher than hydrogen. Is that correct?

    Does anyone here have info on how the elements above iron came/come to be?
  2. jcsd
  3. Jun 4, 2009 #2


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    You're correct: iron has the highest binding energy per nucleon, so it costs energy to fuse it into heavier elements, and the end of the line for a heavy star (light stars usually have contracted long before this point) is theorized to be silicon burning:

    At this point, the star either collapses into a neutron star, or a black hold, becoming a supernova in the process. The energy released in the process of blowing off the outer layers of the star supplies the energy required to fuse iron into heavier elements via supernova nucleosynthesis:

    And hence the expression that we're all made of star dust. IANAAP (I am not an astrophysicist) however.
  4. Jun 4, 2009 #3
    Thanks MAT
    Any ideas on the energy difference in the fusion process itself and the energy generated in the blowing off process?
  5. Jun 5, 2009 #4
    Sorry MAT. Only just read the link you provided. Thx for that.
    It talks about what I asked.

    Just another related question.
    Is there any deliberation among scientists of the possibility of some production of higher elements during the high energies present during the big beginning.
    Or is it considered to only have been an orderly process towards the production of hydrogen alone?
    Did our universe initially only contain hydrogen until stars began to form or would there already have been some higher elements already present?
  6. Jun 5, 2009 #5


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    According to conventional big bang models, the production of elements during the nucleosynthesis era of the universe was as follows:
    75% Hydrogen
    ~25% Helium 4
    .01% Deuterium
    Trace amounts of lithium and beryllium

    There just wasn't enough time to fuse anything more complex than that.

    There's a lot of evidence to support the fact that this is the approximate element ratio pre-stellar nucleosynthesis, so it's quite accepted among scientists.

    Reference: http://en.wikipedia.org/wiki/Big_Bang_nucleosynthesis
  7. Jun 5, 2009 #6
    Thanks Nabe
  8. Jun 5, 2009 #7
    Source: http://en.wikipedia.org/wiki/SuperNova
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