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Photoelectric effect: the emission of electrons from a metal plate caused by light quanta – photons 1926 Gilbert N. Lewis letter which brought the word "photon" into common usage. The word quanta (singular quantum, Latin for how much) was used before 1900 to mean particles or amounts of different quantities, including electricity.
These photons were sufficiently energetic that they could react with each other to form pairs of electrons and positrons. Likewise, positron–electron pairs annihilated each other and emitted energetic photons: γ + γ ↔ e + + e −. An equilibrium between electrons, positrons and photons was maintained during this phase of the evolution of ...
Photons with high photon energy can transform in quantum mechanics to lepton and quark pairs, the latter fragmented subsequently to jets of hadrons, i.e. protons, pions, etc.At high energies E the lifetime t of such quantum fluctuations of mass M becomes nearly macroscopic: t ≈ E/M 2; this amounts to flight lengths as large as one micrometer for electron pairs in a 100 GeV photon beam, while ...
LET has therefore no meaning when applied to photons. However, many authors speak of "gamma LET" anyway, [6] where they are actually referring to the LET of the secondary electrons, i.e., mainly Compton electrons, produced by the gamma radiation. [7] The secondary electrons will ionize far more atoms than the primary photon. This gamma LET has ...
Photons have the largest range of energy and central in a variety of energy conversions. Photons interact with electric and magnetic entities. For example, electric dipole which in turn are excited by optical phonons or fluid particle vibration, or transition dipole moments of electronic transitions.
This is the basic approach of QED. To calculate the probability of any interactive process between electrons and photons, it is a matter of first noting, with Feynman diagrams, all the possible ways in which the process can be constructed from the three basic elements. Each diagram involves some calculation involving definite rules to find the ...
Photons that don’t easily interact with each other, for example, can be used in communication to offer near distortion-free transfer of information at light speed. But sometimes, we do want ...
Virtual photons are responsible for Lamb shift, which is a small shift in the energy levels of hydrogen atoms caused by the interaction of the atom with virtual photons in the vacuum. They are also responsible for the Casimir effect , which is the phenomenon of two uncharged metallic plates being attracted to each other due to the presence of ...