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Annihilation and energy occurance

  1. Sep 19, 2010 #1
    Can someone be precise and tell how much energy is released when annihilation occurs....let's say proton-antiproton(i.e in MeV),also is there some missing energy in it that is not detected(i.e difference between predicted and observed results in energy generation)
     
  2. jcsd
  3. Sep 19, 2010 #2

    mathman

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    In general, annihilation ends up with two photons, each with the energy equivalent to the mass (E=mc2) of one of the particles involved.
     
  4. Sep 19, 2010 #3

    Drakkith

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    I believe the total amount of energy released would be equal to the sum of the two particle masses/energy. An at rest proton and anti-proton would release 2 x 0.938 GeV/c2 in energy in the form of new particles. (Since 0.938 GeV/c2 is the rest mass of a proton.)

    If you add energy into the particles before they annihilate, such as by accelerating them, they will release more energy.
     
  5. Sep 20, 2010 #4

    why??
     
  6. Sep 20, 2010 #5

    Dale

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    Because the system has more energy and energy is conserved.
     
  7. Sep 20, 2010 #6
    Yeah but can someone give numbers?(i.e in MeV how much more is detected)
     
  8. Sep 20, 2010 #7

    Dale

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    Only if you give numbers for how much more energy is added in KE. The detected energy is equal to the sum of the mass energy plus the added KE.
     
  9. Sep 20, 2010 #8
    Two or three, depending on the spins of the original particles. See http://en.wikipedia.org/wiki/Positronium#States".
     
    Last edited by a moderator: Apr 25, 2017
  10. Sep 20, 2010 #9

    Drakkith

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    What is KE exacly?
     
  11. Sep 20, 2010 #10

    Dale

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    Kinetic energy.
     
  12. Sep 20, 2010 #11

    Drakkith

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    Of course! It all seems so simple now!!
     
  13. Sep 23, 2010 #12
    Ok Ok...but can anyone tell the quantity of energy we get during annihilation is "HOW MANY TIMES" that of fusion?
     
  14. Sep 23, 2010 #13

    Dale

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    You really will need to be more specific than that. There are a lot of different fusion reactions, each one with a different yield.

    For the proton-proton chain which dominates the fusion in our sun converts about 0.7% of the mass into energy. So proton-antiproton annihilation releases about 143 times more energy.

    http://en.wikipedia.org/wiki/Proton-proton_chain
     
    Last edited: Sep 23, 2010
  15. Sep 23, 2010 #14

    K^2

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    The number of photons can vary, with low numbers being more likely, and will depend on net angular momentum. If particle-anti-particle pair has angular momentum of 1, for example, at least 3 photons have to be emitted. (Odd number, 1 being forbidden.) Though, for most (all?) particles, the probability of the pair emitting a single photon first, and decaying to a 0 orbital momentum state before annihilation is greater.
     
  16. Sep 24, 2010 #15
    Thanks for the numbers...but at the start of this thread I was looking for numbers in "Mega Electron Volts" and a comparison then,
     
  17. Sep 24, 2010 #16

    Dale

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    Drakkith gave you the numbers in post #3.
     
  18. Sep 24, 2010 #17
    the answer your demanding is dependent on the input variables, like anything else. KE is just one of the input, more would include the angle of interaction if it took place in a 3D model.
     
  19. Sep 24, 2010 #18
    Few more questions,

    1) What is the comparison of strong force to electromagnetism in a particle (let's say in proton), i.e how much is the strong force present as compared to em force (let's hypothetically assume releasing strong force creates 100 MeV energy, how much energy will be created releasing em force)?
     
  20. Sep 25, 2010 #19

    Dale

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    The electromagnetic force is what holds together molecules, so "releasing em force" is a chemical reaction. There are many different chemical reactions, you need to specify which chemical reaction you are interested in and any relevant conditions.

    The strong force is what holds together nuclei, so "releasing strong force" is a nuclear reaction. There are many different nuclear reactions, you need to specify which nuclear reaction you are interested in and any relevant conditions.
     
  21. Sep 25, 2010 #20

    Drakkith

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    Fusion of Tritium and Deuterium releases about 17.6 MeV in energy, thanks to the strong nuclear force. This is thousands of times more energy than one reaction between oxygen and gasoline in an engine.
     
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