Slide 2 of 48
Notes:
So far we have seen processes which lead to the production of X-rays. Now we consider processes which absorb radiation, ie. lead to the removal of photons from a beam. For example, one these processes is scattering.
Every process responsible for the emission of radiation has a corresponding absorption process.
Photoionization leads to recombination of the removed electron, thus photoionization removes X-ray photons - also extreme UV photons - and dominates in these bands.
The two forms of electron scattering, Thomson scattering and Compton scattering, remove photons from the line of sight. In Thomson scattering, the photon energy is much lower than the rest mass of the electron and is just deflected. In Compton scattering, the photon effectively transfers some of its energy to the electron, thus light is absorbed.
At very high energies, photons can collide with ambient photons and form an electron-positron pair, ie photon energy is lost and particles are formed. In the inverse process, electrons and positrons can annihilate each other, emitting gamma-rays.
In synchtron self-absorption, the photons produced by the spiralling of electrons in the magnetic field, are then absorbed by those same electrons.
