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Spontaneous nuclear fission

  1. Jun 17, 2013 #1
    I am confused about spontaneous fission. My basic understanding is that like α-decay the tunnel effect is responsible. We have a potential barrier caused by the superposition of surface tension energy and coulomb potential through which an energised nuclear fragment can tunnel with a certain probability.

    How does the potential barrier of the nucleus relate to its binding energy? I have read that in reality it is only very large nuclei that undergo spontaneous fission; these nuclei have have lower binding energies per nucleon. How does reduction in B/A effect size of potential barrier? Also in class we have derived the tunneling probability

    [itex]T \propto e^{-2G}[/itex]

    where G is the Gamov funktion. I have read that [itex]G \propto m[/itex] and that heavier particles/fragments have lower tunneling probability that is why α-decay is much more common than spontaneous fission of heavy nuclei. If so why are heavy nuclei more likely to fission spontaneously than lighter ones?
     
  2. jcsd
  3. Jun 17, 2013 #2
  4. Jun 17, 2013 #3
    thanks but I have already read those pages enough :)
     
  5. Jun 17, 2013 #4

    anorlunda

    Staff: Mentor

    Here is a speculation. Of elements heavier than iron, the heavier the element the less binding energy per nucleon.

    Of course elements lighter than iron can't spontaneously fission at all.
     
  6. Jun 17, 2013 #5
    just to add to what anorlunda already said , heavy nuclei can fission spontaneously and deliberately because they are unstable to begin with , it has to do with the proton neutron number as it gets too big the nuclear force which holds everything together ( like glue) is having a hard time to hold the big structure together and it can break apart.
    Small nuclei which have few protons and neutrons ( Hydrogen being the smallest one proton one electron) are very sable , few particles holding strongly together.
     
  7. Jun 18, 2013 #6
    thanks for the replies!

    so these large nuclei are unstable to begin with because the binding energy per nucleon drops significantly whilst coulomb repulsion increases causing strong oscillations/deformation in the ground state?

    also I couldn't find a definite answer to this: is the height of the potential barrier Ef above the ground state equal to the binding energy Eb ? are they one and the same? here is what I mean

    http://www.kutl.kyushu-u.ac.jp/seminar/MicroWorld3_E/3Part3_E/3P33_E/fission_barrier_E.jpg
     
  8. Jun 18, 2013 #7
    as for the first one the answer is yes.
    as for the second i will let some more experienced people comment , but as far as I know you can tell how strongly something was held together by calculating how much force it took you to break it apart , now to my understanding this would also be the case to your question number too and I tend to think the answer should be yes.
     
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