A Query about Pair Production and Electron-Positron Annihilation

In summary, according to the experts, it is possible for an electron-positron pair to be produced by a high-energy photon, but it is very rare and the odds of the pair annihilating with each other are very small. This would result in the loss of the original electron.
  • #1
Cambienta
2
0
After an electron-positron pair is produced by a high-energy photon hitting the nucleus of an atom, is it possible for the produced positron to annihilate with a bound electron from the very same atom it was produced in? In this situation, what would happen to the produced electron--would it be captured by the atom to replace the lost electron?

I've been wondering about this for a while, and I've only ever been able to reason that the first scenario would be possible under extremely rare circumstances. Really rare. But I'm not entirely sure that such a thing would be possible under ANY circumstances. I've asked around and done searches, but have only been able to find that it is possible for a positron to annihilate with a bound electron, and that the produced particles don't necessarily have to annihilate with each other, not necessarily that the two processes can be linked and occur subsequently.

I'm wondering what you all might think on the matter?
 
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  • #2
Cambienta said:
After an electron-positron pair is produced by a high-energy photon hitting the nucleus of an atom, is it possible for the produced positron to annihilate with a bound electron from the very same atom it was produced in? In this situation, what would happen to the produced electron--would it be captured by the atom to replace the lost electron?

I've been wondering about this for a while, and I've only ever been able to reason that the first scenario would be possible under extremely rare circumstances. Really rare. But I'm not entirely sure that such a thing would be possible under ANY circumstances. I've asked around and done searches, but have only been able to find that it is possible for a positron to annihilate with a bound electron, and that the produced particles don't necessarily have to annihilate with each other, not necessarily that the two processes can be linked and occur subsequently.

I'm wondering what you all might think on the matter?

Draw the Feynman Diagrams for both cases, they are not the same, one is more complected, less probable?

On the other hand a large Z atom will have lots of electrons which increases likelihood of the more complicated event?
 
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  • #3
The half-life of positronium is on the order of nanoseconds or longer. In a nanosecond, a relativistic electron will travel ~10 cm. Since this is 10^9 times greater than the size of an atom, I would think that the probability of annihilation before it left the vicinity of the original atom would be on the order of 10^-9.
 
  • #4
Cambienta said:
After an electron-positron pair is produced by a high-energy photon hitting the nucleus of an atom, is it possible for the produced positron to annihilate with a bound electron from the very same atom it was produced in? In this situation, what would happen to the produced electron--would it be captured by the atom to replace the lost electron?
Sure. Why not. The probability of positron annihilation in flight is plotted on page 385 of Heitler "Quantum Theory of Radiation" 3rd edition. Also read Section 27 on page 268. The atomic electron is close by, so it could annihilate in the same atom. It is not necessary to stop positrons and create positronium for them to annihilate. The other electron is going too fast to get captured in an atomic bound state.
Bob S
 
  • #5
Thanks! Gosh, I thought I'd replied to this. I really appreciate the answers. Bob, I picked up the book you mentioned (I found it quite cheap online), and it's been helpful.

Thank you again for your replies.
 

FAQ: A Query about Pair Production and Electron-Positron Annihilation

1. What is pair production and electron-positron annihilation?

Pair production is a process in which a photon (a particle of light) is converted into an electron and a positron (an anti-electron). This typically occurs in the presence of a strong electric field. Electron-positron annihilation is the opposite process, in which an electron and a positron collide and their mass is converted into energy in the form of photons.

2. How does pair production and electron-positron annihilation relate to each other?

Pair production and electron-positron annihilation are inverse processes, meaning they are two sides of the same coin. In pair production, a photon is converted into an electron and a positron, while in annihilation, an electron and a positron collide and produce photons. These processes are governed by the laws of conservation of energy and momentum.

3. What are some applications of pair production and electron-positron annihilation?

Pair production and electron-positron annihilation have many applications in modern technology. For example, in medical imaging, positron emission tomography (PET) uses the annihilation of positrons to produce images of the body's tissues and organs. In particle accelerators, pair production is utilized to create high-energy electrons and positrons for experiments. These processes also play a role in the creation of new particles in the early universe.

4. How is pair production and electron-positron annihilation studied in the laboratory?

In the laboratory, pair production and electron-positron annihilation can be studied using particle accelerators or high-energy photon sources. These experiments involve creating a strong electric field or colliding electrons and positrons at high energies to observe the production and annihilation of particles. The resulting particles and photons can then be detected and studied to better understand these processes.

5. Are there any current developments or research in the field of pair production and electron-positron annihilation?

Yes, there is ongoing research in this field to better understand the fundamental properties of particles and their interactions. Scientists are also exploring potential applications of these processes, such as energy production and advanced imaging techniques. Additionally, advancements in technology have allowed for more precise and detailed experiments, leading to new discoveries and insights into pair production and electron-positron annihilation.

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