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By high energy I mean 100+ MeV gamma rays. I think that at this energy of photons, pair production is the dominating absorption process.

So, as known, in pair production an electron and a positron are produced and any excess energy of the photon over the rest mass of the electron and the positron will be in the form of the kinetic energy of the new electron and positron.

So now, how will the electron and positron end up in a dense material ? like will the electron come to a stop releasing its in energy in the material and thus heating it up ? or will it escape the material ?

I am assuming using the attenuation length of Lead at this gamma ray energy as the absorbing material.

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What material thickness are you considering? The electron will deposit its energy in about 1 cm. I don't know about the positron range. –  fffred Aug 22 '13 at 21:16
    
For positrons it's actually not too different (ccsenet.org/journal/index.php/apr/article/view/8088). However, most of the energy of the electron or positron will be lost by Bremsstrahlung above 10 MeV. That does not sound very easy to calculate how much of that is actually absorbed. –  fffred Aug 22 '13 at 21:34
    
I mentioned "attenuation length" of lead, which is about 1 cm at this energy I think. But also I think it depends on the kinetic energy of the electron, so maybe in this case more than 1 cm is needed since much of the gamma ray energy is on the form of kinetic energy for the electron ? –  Abanob Ebrahim Aug 22 '13 at 21:34
    
The gamma ray will mostly provide its energy to the kinetic energy of e and p, but then they create bremsstrahlung, which does not deposit so much energy directly in the material. I think you need a code to simulate that. This is not straightforward. –  fffred Aug 22 '13 at 21:37
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If I may say so, you have asked a series of very vague questions about interaction of radiation with unspecified materials of unspecified configuration. These kinds of questions come up in experimental nuclear and particle contexts all the time only they are much better specified. Both providing back-of-the-envelope estimates and then preparing proper Monte Carlo calculations when needed are pretty straight forward work than any graduate student can do easily, but the problem has to be specified which you have not done. The only answer to this as asked is "everything ends up as heat". –  dmckee Aug 22 '13 at 22:35

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