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I How many barns above could make nuclear reaction rate 100%?

  1. Apr 12, 2016 #1
    All guys know the importance of cross section. In a sense, it stands for the possibility of a reaction.
    I am wondering how many barns above could make nuclear reaction rate almost 100%?
    Generally speaking, the cross section can span a couple of decades order of magnitude, e.g. 10^-10 to 10^6 barns.
    I speculate the answer maybe 100Kb+.
     
  2. jcsd
  3. Apr 12, 2016 #2

    mfb

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    There is no direct relation between a cross section and a reaction rate. Also, what does "100%" mean: 100% of what?
    You might be interested in cross section ratios.

    Cross sections like 10-15 barns are not unusual for things like Higgs in specific decay channels or double Higgs production, and dark matter cross sections are even smaller.
     
  4. Apr 12, 2016 #3
    For example, 7Li(p,n)7Be, at 1910Kev of proton beam, the cross section 590mb, statistics shows every 100,000 protons, only 1 proton is used in the said reaction. So I guess if a reaction with 100,000b above cross section, then all bombarding protons will be consumed in reaction.
     
  5. Apr 12, 2016 #4

    mfb

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    Never all, but the fraction can get close to 1. You always have some other processes with their own cross sections competing.
     
  6. Apr 12, 2016 #5
    Is there a way to manually increase specific cross section? Looking up recognized data table, always feel disappointed with those so tiny sigma.
     
  7. Apr 13, 2016 #6
    An example of a reaction with fraction very close to 1 is positron annihilation. Positron is stable, so it has few options other than annihilation.
    How common reaction is positron capture?
     
  8. Apr 13, 2016 #7

    mfb

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    You cannot change cross sections.
    Positrons have a positive charge, so at low energies the probability is "zero". At high energies, inelastic reactions have a higher probability.
     
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