Electron - Positron Annihiliation

In summary, when positrons collide, they undergo complete annihilation and produce two or more gamma rays. The energy released is governed by the equation E = mc^2 and can be calculated using this equation. For 1 mole of any substance undergoing beta + decay, the energy released is 98 GJ. This energy is released in the form of photons, which are used in nuclear reactors for energy production. The energy released in one annihilation is very small, but a large number of these reactions can provide a significant amount of energy.
  • #1
qwertyuiop23
9
0
I know that positrons are produced by beta + decay and I know that they are antimatter. My question now comes to what happens when the collide. I know that should be complete annihiliation and the most likely outcome is the production of two or more gamma rays. My question comes when trying to calculate the energy of those rays. Should the energy produced be governed by E = mc^2? If it does and I have done my calculations then the energy released by positron - electron annihiliation 1.6*10^-13 J of energy is released which is not a lot of energy but I would have thought I would see some trace of this energy. And if this theory is then applied to 1 mol of any substance that beta + decay (since the production of positrons is in a 1:1 ratio to the substance decaying) I calculated that we get 9.8*10^10 which is 98 GJ. I have no idea how much that is in relation but it seems a lot.

Could someone verify what I have done here and I haven't made any misconceptions. And if I am correct then where does the 98GJ go when the atom decays.

Cheers
~Qwertyuiop23
 
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  • #2
The energy is released in the form of photons, the massless "particles" which make up light. For photons the energy depends on the frequency f through E = h f (where h is another physical constant, just like c). Although the amount of energy per annihilation is very very tiny, a lot of these reactions can provide a lot of energy. This is used in nuclear reactors for example - if you look up some of them on Wikipedia you can see their energy production in the info box, this is of order 1016 J.
 
  • #3
You are correct. Some nucear beta decays emit positrons. Positrons sometimes annihilate with electrons before stopping, but most stop and form an electron-positron "atom" called positronium, and annihilate after a few nanoseconds. The energy released in one annililation is about 1.6 x 10^-13 Joules, and is in the form of two opposing 511-Kev photons. A mole of these annilations would release about 98 GJ of energy. using 120 MJ as the energy in 1 gallon of gasoline, 98 GJ is equivalent to the energy in about 800 gallons of gasoline.
 

Related to Electron - Positron Annihiliation

1. What is electron-positron annihilation?

Electron-positron annihilation is a process in which an electron and positron (the antiparticle of an electron) collide and are converted into energy in the form of two photons (particles of light).

2. How does electron-positron annihilation occur?

Electron-positron annihilation occurs when an electron and positron come into close proximity with each other and interact through the electromagnetic force. This causes the particles to annihilate, releasing energy in the form of photons.

3. What is the significance of electron-positron annihilation in particle physics?

Electron-positron annihilation is significant in particle physics because it provides a way to study the properties of particles and the fundamental forces that govern their interactions. This process allows scientists to create and observe new particles that may only exist for a brief moment before decaying into other particles.

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

Yes, electron-positron annihilation can occur in nature through various processes, such as in high-energy collisions between particles in the atmosphere or in particle accelerators. It can also occur in stars, where high temperatures and pressures can create the conditions for electron-positron annihilation to take place.

5. How is electron-positron annihilation used in practical applications?

Electron-positron annihilation has practical applications in medical imaging, specifically in positron emission tomography (PET) scans. In PET scans, a positron-emitting radioactive substance is injected into the body, and when the positrons collide with electrons in the body, they undergo annihilation, producing photons that can be detected and used to create images of the inside of the body.

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