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Interactions of high energy photons with matter

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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    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

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