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It is the ratio of the number of electrons emitted to the number of incident photons. [1] This property depends on the wavelength of light being used to illuminate the photocathode. For many applications, QE is the most important property as the photocathodes are used solely for converting photons into an electrical signal.
The threshold temperature for production of electrons is about 10 10 K, 10 13 K for protons and neutrons, etc. According to the Big Bang theory, in the early universe, mass-less photons and massive fermions would inter-convert freely.
These are accelerated by an electrostatic field where they strike a phosphor coated screen, converting the electrons back into photons. Intensification of the signal is achieved either through acceleration of the electrons or by increasing the number of electrons through secondary emissions, such as with a micro-channel plate. Sometimes a ...
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 ...
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.
For photons with high photon energy (MeV scale and higher), pair production is the dominant mode of photon interaction with matter. These interactions were first observed in Patrick Blackett 's counter-controlled cloud chamber , leading to the 1948 Nobel Prize in Physics . [ 3 ]
Photons are massless particles of definite energy, definite momentum, and definite spin. To explain the photoelectric effect , Albert Einstein assumed heuristically in 1905 that an electromagnetic field consists of particles of energy of amount hν , where h is the Planck constant and ν is the wave frequency .
Conservation of energy and linear momentum forbid the creation of only one photon. (An exception to this rule can occur for tightly bound atomic electrons. [1]) In the most common case, two gamma photons are created, each with energy equal to the rest energy of the electron or positron (0.511 MeV). [2]