AQA AS physics question

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1. Sep 4, 2013

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?

2. Sep 4, 2013

Staff: Mentor

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

3. Sep 4, 2013

125.6

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!

4. May 21, 2017