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Interactions of high energy photons with matter
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Cross section. Cross-section per atom (or per electron) = ?Attenuation length l = 1/n? , where n is density of atomsAttenuation of beam I = I0 exp(-x/l)For materials, we often use the attenuation coefficient, ?, which is the cross second per mass (cm2/g)Then attenuation length l = 1/n? = 1/??, w
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Interactions of high energy photons with matter
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Presentation Transcript
1. Interactions of high energy photons with matter Cross section/attenution length/optical depth
Photoelectric absorption
Compton scattering
Electron-positron pair production
2. Cross section
3. Three interactions Photoelectric absorption
Photon is absorbed by atom
Electron is excited or ejected
Compton scattering
Photon scatters off an electron
Pair production
Photon interacts in electric field of nucleus and produces an e+ e– pair
4. Photoelectric cross section in Xe
5. Photoelectric absorption
6. Photoelectric absorption
7. Interstellar absorption
8. Compton scattering
9. Compton scattering
10. Pair Production
11. Photon Cross Sections in Nitrogen
12. Photon Cross Sections in Lead
13. Reading Longair: 4.1, 4.2, 4.3 (skip 4.3.3, 4.3.4), 4.4