Positron-electron annihilation

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In summary: Two gamma rays which are emitted simultaneously and have enough energy will generate electron-positron pairs. However, it does not have to be the same photons which are emitted in the annihilation process.
  • #1
Physicsissuef
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Do the gamma rays (from positron-electron annihilation) must interact to have reversible reaction? I read in my textbook that this reaction is reversible? Is that true?
The reaction:


[tex]
^{0}_{-1}e+ ^{0}_{+1}e \rightarrow 2 \gamma
[/tex]
 
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  • #2
In principle, the reverse is possible. It is just difficult to achieve experimentally.
 
  • #3
Does the gamma rays must interact?
 
  • #4
Physicsissuef said:
Does the gamma rays must interact?


Yes. Right after the big bang, when the universe was very small and very hot, gamma-gamma reactions were taking place not only for electron-positron pairs, but heavier particle-antiparticle pairs (such as proton-antiproton or neutron-antineutron) also.
 
  • #5
but how those gamma rays will interact them selfs when they are going parallel to each other?
 
  • #6
electron positron pair

You should visit wiki pedia to check the phenomenon of pair production; also if I am not wrong then it is not necessary to for the production of electron and positron pair that we should annihilate two gamma rays. A single gamma (photon) ray having energy greater then 1.02 Mev can be splitted into electron positron pair, when ever an attempt to stop it with the help of nuclei of heavy element is made. Moreover two gamma rays moving parallel to each other, I don’t think they will annihilate into electron positron pair.
 
  • #7
Physicsissuef: It does not have to be the same photons which are emitted in the annihilation process of the electron and positron. Any two photons which have enough energy may produce electron - positron pairs.

kosher: There is a difference between gamma-gamma reactions and pair production. Gamma-gamma reactions are a photon interacting with another photon. In pair production, one has a photon of E > 1.022MeV producing a electron - positron pair, this reaction MUST take place near an atomic nucleus or an atomic electron.
 
  • #8
Here is http://pic.mkd.net/images/1016371213.jpg" [Broken] from my book. That's why I said they are parallel.
 
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  • #9
Anybody knows, please? How will the reverse reaction go?
 
  • #10
Physicsissuef said:
Anybody knows, please? How will the reverse reaction go?

It depends on how the initial electron-postiron pair annihilates, remember our discussion in the other thread? Initial momentum = final momentum & initial energy = final energy
 
  • #11
Yes, but for the reverse reaction they must interact, how will they interact when they are parallel?
 
  • #12
Post #7:

It does not have to be the same photons which are emitted in the annihilation process of the electron and positron. Any two photons which have enough energy may produce electron - positron pairs is good enough.
 
  • #13
Physicsissuef said:
Here is http://pic.mkd.net/images/1016371213.jpg" [Broken] from my book. That's why I said they are parallel.

That picture is misleading. They should not be parallel.
 
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1. What is positron-electron annihilation?

Positron-electron annihilation is a process in which a positron (a positively charged particle) and an electron (a negatively charged particle) collide and are converted into two photons (particles of light). This process can only occur when the total energy of the positron and electron is equal to or greater than the combined mass of the two particles.

2. How is positron-electron annihilation used in scientific research?

Positron-electron annihilation is used in various fields of scientific research, such as nuclear physics, material science, and medical imaging. It can provide valuable information about the structure and properties of materials, and can also be used to study the behavior of particles in high-energy environments.

3. Can positron-electron annihilation be observed in nature?

Yes, positron-electron annihilation can occur in certain natural processes, such as radioactive decay and high-energy collisions between particles in space. It is also an important process in the formation of antimatter in the early universe.

4. What are the potential applications of positron-electron annihilation technology?

Positron-electron annihilation technology has potential applications in various fields, including medical imaging (such as positron emission tomography), materials testing, and energy production (through the use of antimatter as a potential fuel source).

5. Is positron-electron annihilation a reversible process?

No, positron-electron annihilation is an irreversible process. Once the positron and electron collide and annihilation occurs, they are converted into photons and cannot be re-created as particles. However, the photons can be absorbed and converted back into particles through other processes.

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