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Why energy absorbing after Fe and energy realising before Fe ?

  1. Dec 23, 2009 #1

    Edi

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    Thats about it - why does the nuclear fusion release energy when fusing lighter elements, but absorbs energy for heavier elements?
    Something to do with the week nuclear forces low range and after Fe it simply crosses that range? But... every hadron in the nucleon has the week force, with its limited range, ...
    Or that the week force doesn't add up (limited range) while EM does? But in that case what does make it all "stick", why does giving more energy make it stick?

    .. waiting some answers, so I can get clearer on what questions to ask.
     
  2. jcsd
  3. Dec 23, 2009 #2

    Astronuc

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    I believe one is referring to binding energy - http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin.html#c1

    Fe and Ni isotopes are among the most tightly bound (stable) nuclei, and there is little between neighboring nuclei.

    For the lightest elements have lesser binding energy per nucleon comparted to isotopes near Fe, so fusion light elements to heavier elements releases energy. In contrast the heaviest elements have lesser binding energy per nucleon, and the release energy by fissioning into lighter nuclei, e.g. U-235 (+ n) fissioning to Rb-90 + Cs-143 + 3 n.
     
  4. Dec 24, 2009 #3

    Edi

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    Did you mean that lighter elements have more binding energy? Because you both light and heavy elements can't have lesser.. ;)

    .. the nuclear binding energy, that is the week force, right?
    Light nuclei after fusing have spare, left-over energy, but heavier doesn't have enough, so it needs to absorb it?
    Then, by increasing the kinetic energy of particles gives more energy to the reaction, but how does the kinetic energy transfers to increased week force??
     
  5. Dec 24, 2009 #4

    Astronuc

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    I would recommend calculating the total binding energy and binding energy per nucleon for various nuclei.

    Binding energy is actually the energy required to remove one or more nucleons or groups of nucleons (e.g., alpha particle), or the energy to dissociate a nucleus into its constituent nucleons. The total binding energy would be (A-1)*BE/nucleon, but for most practical applications, one refers to BE/nucleon or the BE/(last nucleon).

    The BE for the last nucleon is on the order of MeV, and one can use gamma rays, neutrons or other high energy particles to 'knock out' nucleons or particles from nuclei.

    Basically light nuclei like d,t, He-3, Li-6 and others fuse and reconfigure. The excess energy is manifest in the nuclear products. A reaction of p + B11 is more accurately fission, since although p fuses with B11, the excited nucleus fission to form 3 alpha particles.

    As for forces, it has to do with a balance of nuclear and EM/Coulomb forces. The weak force governs the beta/positron decay.
    http://hyperphysics.phy-astr.gsu.edu/hbase/forces/funfor.html
     
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