Can a 2MeV photon produce a proton-antiproton pair?

• 125.6
In summary, when a photon of energy 2MeV collides with matter, it can produce an electron-positron pair due to the rest energy of an electron and a positron being less than 2MeV. However, it cannot produce a proton-antiproton pair as their rest energy is higher than 2MeV. This ensures conservation of energy. In the given example, the total energy of the positron and electron is 1.180MeV, taking into account the rest energy and kinetic energy of the particles.
125.6
Hi all - just a bit confused about an answer in the AQA AS Physics textbook:

'Explain why a photon of energy 2MeV could produce an electron - positron pair, but not a proton - antiproton pair'

'The rest energy of an electron and a positron is less than 2MeV but not for a proton-antiproton pair, So pair production can happen for an electron and positron'

I don't understand the answer, so pair production can not happen if the rest energy of the particle-antiparticle pair is less than the minimum energy of the carrier photon? is this correct?

125.6 said:
I don't understand the answer, so pair production can not happen if the rest energy of the particle-antiparticle pair is less than the minimum energy of the carrier photon? is this correct?

Yes (unless there is some other source of energy coming in as well as the photon). Otherwise, conservation of energy would be violated.

Nugatory said:
Yes (unless there is some other source of energy coming in as well as the photon). Otherwise, conservation of energy would be violated.

Ok great, thanks for that.

I have another question if you don't mind? (i'm self studying physics so i might have quite a few :( )

The question says: The rest energy of an electron is 0.511 MeV; a positron collides with an energy of 0.158 MeV of energy, calculate the total energy of the positron and the electron' with an answe of 1.180 MeV

I've tried using E=hf but that gives me an answer of around 0.7 MeV?? Sorrry!

The rest energy of the positron must be taken into account. As it is the antiparticle of the electron it will have the same rest mass/energy as the electron, which the question tells us is 0.511MeV. The positron has a kinetic energy of 0.158Mev, so adding this to the rest energy of the positron (0.551MeV) gives us an energy of 0.669MeV. The total energy of the positron is 0.669MeV, add this to the energy of the electron (0.511MeV) to give an answer of 1.180MeV.

1. What is the format of the AQA AS physics question?

The AQA AS physics question is typically a written paper consisting of multiple-choice, short answer, and longer response questions. The paper is usually divided into sections and may also include practical or data analysis tasks.

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The total number of marks for the AQA AS physics question varies each year, but it is typically between 70-80 marks. This makes up a significant portion of the overall grade for the AS physics exam.

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The AQA AS physics question covers a wide range of topics including mechanics, electricity, waves, particles, and radiation. It also includes practical skills such as data analysis, experimental methods, and mathematical skills.

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