Attenuation- Radiography

Attenuation consisting of both scattering and attenuation. In classical scattering is also known as elastic scattering, this occurs when an incident photon bounces off an atom. The photoelectric effect is inversely proportional to the kV cubed and is proportional to the atomic number cubed. The photon is completely absorbed. The ejected electron is known as the photoelectron. In Compton scatter the incident photon is both absorbed and scattered. The ejected electron is known as a recoil electron which is scattered in the forward direction. The photon has a longer wavelength than the incident photon due to loss of energy. Pair production never occurs in diagnostic radiography but does occur in radiotherapy radiography as the energy required for it to be initiated is 1.02 MeV. This process is inversely proportional to energy. A positron and a negatron are produced; the positron is annihilated when it collides with an electron.

Electrons are boiled off from the cathode of an x-ray tube. They are accelerated to high speed by a potential difference to strike the anode also known as the target. The incident electron interacts with an inner shell electron of the target material this creates a vacancy in the shell. An electron from an outer shell fills that space and releases energy in the form of an x-ray of characteristic wavelength for the target material. When an x-ray is release by a L shell electron falling into a K shell hole, this is known as a K alpha emission, a M to K shell transition is known as a K beta emission. If an incident electron interacts with the nuclear field of a target atom, the electron is slowed down and releases energy in the form of an x-ray, this can occur for energies up to the maximum kV and will result in the minimum wavelength of radiation. This process is also known as braking radiation or bremsstralung.