What happens when gamma rays with ultra-high energies interact with matter?

In summary, photons with energies over 1 Joule interact with matter in a few different ways, but the dominant process is pair production. Higher energy photons produce more lower energy photons, but at very high energies only photon-gluon fusion becomes relevant.
  • #1
neanderthalphysics
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TL;DR Summary
1x10e11 eV and above
What sort of properties would you expect from gamma rays, as you increase their energy, and why? Would they penetrate high Z-matter more easily? What would be the outcome of the interactions? Do you expect photoelectric and Compton scattering processes to become negligible, and the dominant interaction mechanism becomes pair production?

On a macroscopic scale, what do you think would happen if photons with energies of something like 1J each interacts with matter? A very small antimatter explosion from pair production and subsequent annihilation?
 
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  • #2
Pair production is dominant already at the GeV range and it stays that way. You get electromagnetic showers with electrons, positrons and photons. Towards the end you get more and more lower energy processes.
 
  • #3
As the energy increases, you have additional absorption channels opening up:
  • Around 10 MeV depending on the target nuclei - photonuclear reactions
  • About 140 MeV - direct pion production
  • About 210 MeV - muon pair production
  • About 300 MeV - a resonance peak of pion production via Δ
  • About 700 MeV - start of hyperon production, like p+γ→Λ+K+
  • About 1900 MeV - nucleon pair production, and soon after hyperon pairs
  • About 3500 MeV - tauon pair production, and soon after charm
  • Around 10 GeV - beauty pair production
  • From 80 GeV - real W and soon after Z bosons.
Is it confirmed that simple electron-positron pair production stays dominant above all the higher energy processes combined at all energies, including their resonance peaks/edges?
 
  • #4
We have photons up to ~2 TeV in the LHC collisions. They make electromagnetic showers as expected. The other processes are not impossible but very rare. Resonances are rare or very narrow, the latter makes them rare for a relevant photon spectrum.
Some of your thresholds are too low, by the way. An 80 GeV photon hitting a nucleus doesn't have 80 GeV center of mass energy with the photon/quark system, it only has something of the order of 10 or even less.
 
  • #5
mfb said:
Some of your thresholds are too low, by the way.

All of them besides the one where "it depends". (And there is no such thing as a "tauon".)

mfb said:
The other processes are not impossible but very rare.

True, but I don't think that gets across how rare is rare. The Bethe-Heitler process goes as 1/m2 so muon pair production at very high energies is 1/40,000 of the electron rate. There's also threshold effects at low and moderate energies: 99.998% of 500 MeV photons don't produce muons.

Even correcting the errors, these additional processes just aren't relevant.

The process that becomes relevant at very high energies is photon-gluon fusion, because that happens with QCD-sized cross-sections, not EM-sized cross-sections. This is still rare: say the 1/1000 rate instead of the 1/100,000+ you might expect from a pure EM process.
 
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Related to What happens when gamma rays with ultra-high energies interact with matter?

1. What are ultra-high energy gamma rays?

Ultra-high energy gamma rays are a type of electromagnetic radiation with the highest known energy levels. They have wavelengths shorter than 10^-11 meters, making them the most energetic form of light.

2. Where do ultra-high energy gamma rays come from?

Ultra-high energy gamma rays are produced by extreme astrophysical events such as supernovae, active galactic nuclei, and gamma-ray bursts. They can also be created by interactions between cosmic rays and matter in space.

3. How are ultra-high energy gamma rays detected?

Ultra-high energy gamma rays are detected using specialized telescopes called imaging atmospheric Cherenkov telescopes. These telescopes use the Cherenkov effect, which is the emission of light when high-energy particles travel through a medium at speeds faster than the speed of light in that medium.

4. What is the significance of studying ultra-high energy gamma rays?

Studying ultra-high energy gamma rays can provide valuable insights into the most extreme and energetic processes in the universe. They can also help us understand the origin and propagation of cosmic rays, which are high-energy particles that constantly bombard the Earth.

5. Can ultra-high energy gamma rays be harmful to humans?

Yes, ultra-high energy gamma rays can be harmful to humans if exposed to high doses. However, the Earth's atmosphere acts as a shield and prevents most of these rays from reaching the surface. Additionally, scientists take precautions when working with these high-energy particles to minimize any potential risks.

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