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Pair production and the Compton effect occur at the level of the electron. [1] When a high frequency photon scatters due to an interaction with a charged particle, there is a decrease in the energy of the photon and thus, an increase in its wavelength. This tradeoff between wavelength and energy in response to the collision is the Compton effect.
Feynman diagram of electron–positron pair production. One must calculate multiple diagrams to get the net cross section. The exact analytic form for the cross section of pair production must be calculated through quantum electrodynamics in the form of Feynman diagrams and results in a complicated function. To simplify, the cross section can ...
English: Plot showing the relative importance of the photoelectric effect, Compton scattering and pair production with different Z and mean photon energy. Data taken from the NIST XCOM database. For any given element (atomic number Z) a star is added at the energy where the cross section value for the process on the right becomes larger than ...
Compton scattering and pair production are examples of two other competing mechanisms. [ citation needed ] Even if the photoelectric effect is the favoured reaction for a particular interaction of a single photon with a bound electron, the result is also subject to quantum statistics and is not guaranteed.
A gamma ray cross section is a measure of the probability that a gamma ray interacts with matter. The total cross section of gamma ray interactions is composed of several independent processes: photoelectric effect, Compton (incoherent) scattering, electron-positron pair production in the nucleus field and electron-positron pair production in the electron field (triplet production).
For highly energetic photons such as X-rays (0.1 keV < < 100 keV) and γ-rays (> 100 keV), three types of interactions are responsible for the energy conversion process in scintillation: photoelectric absorption, [6] Compton scattering, [7] and pair production, [8] which only occurs when > 1022 keV, i.e. the photon has enough energy to create ...
The Feynman diagrams are much easier to keep track of than "old-fashioned" terms, because the old-fashioned way treats the particle and antiparticle contributions as separate. Each Feynman diagram is the sum of exponentially many old-fashioned terms, because each internal line can separately represent either a particle or an antiparticle.
When an ionizing particle passes into the scintillator material, atoms are excited along a track. For charged particles the track is the path of the particle itself. For gamma rays (uncharged), their energy is converted to an energetic electron via either the photoelectric effect, Compton scattering or pair production.