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B What is the heaviest element that a star will fuse?

  1. Jan 16, 2017 #1
    Is Iron the heaviest element a star will fuse through nuclear fusion or will it continue to Iron into a heavier element.
     
  2. jcsd
  3. Jan 16, 2017 #2

    Drakkith

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    I was under the impression that the highest mass element produced in large quantities was nickel-56. However, I keep finding conflicting information from various sources. Some say iron is the highest and some say nickel. I haven't yet found a good source that explains things in any real detail. I'll let you know if I do.
     
  4. Jan 16, 2017 #3

    PAllen

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    Nickel 56 decays into cobalt, then iron.
     
  5. Jan 16, 2017 #4

    Drakkith

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    True, but does nickel have time to do so in the core of a star?
     
  6. Jan 16, 2017 #5
    Going on that notion what woudl the chronological order to element fusion be? (i.e. Hydrogen to Helium, Helium to Carbon etc.)
     
  7. Jan 17, 2017 #6

    PAllen

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    The half lives are both relatively short ( < 7 days, < 80 days). Whether energy/density conditions in a stellar core modify this, I am not sure. Since iron-56 makes up a large majority of planetary iron, I assume most comes from decay of nickel 56 produced in stars.
     
  8. Jan 17, 2017 #7

    fresh_42

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    What I'm curious about is not whether the theoretical end is Fe or not, but to which extend heavier elements are built, simply as an incidental byproduct of high energy collisions.
     
  9. Jan 17, 2017 #8
    The star kills itself when it creates iron, after which it creates many of the heavier elements when it goes supernova; search up 'r-process'.
     
  10. Jan 17, 2017 #9

    Drakkith

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    Yes, iron-56 comes from the decay of nickel-56 (actually cobalt-56, which decays to iron-56), but I don't know how long it takes for enough nickel/cobalt/iron to build up in the core to trigger a collapse and supernova.
     
  11. Jan 17, 2017 #10
  12. Jan 20, 2017 #11

    Chronos

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    Enormous energy is needed to fuse iron or any heavier elements - hence most are formed by supernovae which do have sufficient energy for such processes.
     
  13. Jan 24, 2017 #12
    Get a chart of isotopic masses and relative abundances, like

    https://www.ncsu.edu/chemistry/msf/pdf/IsotopicMass_NaturalAbundance.pdf

    and you can work it out for yourself. For example, a star fuses 4 atoms of hydrogen 1, 4 times 1.007825 = 4.0323
    to get 1 atom of Helium 4, mass 4.002603, and releases
    4.0323 -4.002603 = 0.029697 units of energy.

    Try fusing 1 atom of hydrogen 1, 1.007825, to 1 unit of Iron 56, 55.934942
    to get Iron 57 with mass of 56.935399, and the star releases
    1.007825 + 55.934943 - 56.935399= 0.0073681 units of energy.

    Try fusing 1 atom of carbon 12, 12..00000 , to 1 unit of Iron 56, 55.934942
    to get zinc 68, and the star gets
    12.0000 +55.934942 - 67.924848= minus 0. 01.0094 units of energy.

    If there were still hydrogen in the core, a star could still gain a little energy by fusing Iron and Hydrogen to get NIckel, but by the time Iron has formed, there's a negligible amount of unfused Hydrogen left in the core. All the minus unit energy elements are produced only in a supernova.
     
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