<p>The Compton cross section starts to get reduced significantly only when the photon energy is significant compared to the electron rest energy.  So at that energy scale, for a more isotropic radiation field, you would have to start worrying about some of the photons having enough energy to combine with another photon and create an electron-positron pair.</p>

CC BY-SA 3.0
2016-12-23T16:29:34.290Z
2016-12-23T16:29:34.290Z
Ken G
<p>The answer is <a href="https://en.wikipedia.org/wiki/Pair_production" rel="noreferrer">pair production</a>. Once photon energies exceed 1.02 MeV it is possible to spontaneously create an electron-positron pair in the presence of an atomic nucleus (to conserve momentum). In general for high energy photon interactions with matter you need to consider the photoelectric effect, Compton scattering and pair production. The former is more important at lower energies, the latter at higher energies.</p>

<p>The picture below shows the mass attenuation coefficients for Aluminium and Iron as a function of energy, with the contributions of these three processed identified.</p>

<p><a href="https://i.sstatic.net/NFbG6.png" rel="noreferrer"><img src="https://i.sstatic.net/NFbG6.png" alt="Mass attenuation coefficients"></a></p>

CC BY-SA 3.0
2016-12-23T16:28:35.903Z
2016-12-23T16:35:36.613Z
2016-12-23T16:35:36.613Z
ProfRob
<p>I was reading up on Compton radiation, and a question came up which I could not quite answer.</p>
<p>Compton scattering is known to be less efficient at high energies, due to the fact that the Klein-Nishina cross-section falls off at the high energy end. This means that the Universe is more transparent to Compton radiation at high energies.</p>
<p>What other processes could stop high energy photons from propagating through the Universe (i.e., a process that preferentially stops high-energy photons)?</p>

<radiation><high-energy-astrophysics>
Compton scattering of high energy radiation
user1991
# Compton scattering of high energy radiation

(Asked by: username_0 on 2016-12-23)

I was reading up on Compton radiation, and a question came up which I could not quite answer.

Compton scattering is known to be less efficient at high energies, due to the fact that the Klein-Nishina cross-section falls off at the high energy end. This means that the Universe is more transparent to Compton radiation at high energies.

What other processes could stop high energy photons from propagating through the Universe (i.e., a process that preferentially stops high-energy photons)?

**Tags:** radiation, high-energy-astrophysics

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## 2 answers

### Answer by username_2 on 2016-12-23. Score: 5 | Accepted answer

The answer is [pair production](https://en.wikipedia.org/wiki/Pair_production). Once photon energies exceed 1.02 MeV it is possible to spontaneously create an electron-positron pair in the presence of an atomic nucleus (to conserve momentum). In general for high energy photon interactions with matter you need to consider the photoelectric effect, Compton scattering and pair production. The former is more important at lower energies, the latter at higher energies.

The picture below shows the mass attenuation coefficients for Aluminium and Iron as a function of energy, with the contributions of these three processed identified.

[![Mass attenuation coefficients](https://i.sstatic.net/NFbG6.png)](https://i.sstatic.net/NFbG6.png)


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### Answer by username_1 on 2016-12-23. Score: -1

The Compton cross section starts to get reduced significantly only when the photon energy is significant compared to the electron rest energy. So at that energy scale, for a more isotropic radiation field, you would have to start worrying about some of the photons having enough energy to combine with another photon and create an electron-positron pair.


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