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-   -   How much energy is required to produce the electron-positron pair ... (http://www.physicsforums.com/showthread.php?t=581279)

 vst98 Feb25-12 04:09 PM

How much energy is required to produce the electron-positron pair ...

1. The problem statement, all variables and given/known data
How much energy is required to produce the electron-positron pair in the filed of nucleus (Z=20) if electron is captured to the ground 1s state of the system.

3. The attempt at a solution

I can calculate the energy of the captured electron from

E = - εZ2/(2n2) where ε=me4/hbar2≈27.2eV

E = - 5442eV

Now I have to add this energy to the energy of created positron to have total required energy, right ? But I do not know how to find energy of a positron.

 tiny-tim Feb25-12 04:44 PM

hi vst9! :smile:
Quote:
 Quote by vst98 (Post 3784087) … But I do not know how to find energy of a positron.
won't it be the same as the energy of the electron?

 vst98 Feb26-12 03:03 PM

Re: How much energy is required to produce the electron-positron pair ...

hi tiny-tim !

Yes I think so, then it is the energy and momentum conservation that places a restriction
on the positron to have the same energy as electron , right ?

I was a little bit confused by the "... in the filed of nucleus" part of the question, then
this filed of a nucleus does not change much (except maybe the needed energy).

So, the needed energy for pair creation is E=2*5442=10.88keV

 tiny-tim Feb26-12 04:41 PM

hi vst98! :wink:

right! :smile:

i'm not sure why they mentioned the field (not "filed" :wink:) … it doesn't seem to add anything to the rest of the question :confused:

 vst98 Feb27-12 05:18 PM

Re: How much energy is required to produce the electron-positron pair ...

Ok, thanks !

(yes it is "field" and not "filed" in the original question, my flip error :) )

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