Photon

classification

characteristics

Charge	0 C
proper mass	0 kg
spin	1

in physics one marks the elementary suggestion (quantum) of the quantized electromagnetic field with photon (of Greek φως, phos = light).It is one of the study objects of quantum electrodynamics, the oldest part of the standard model of particle physics. Descriptive spoken photons are „the components of “electromagnetic radiation, like that something like „light particles “. However it may not be forgotten with the fact that all (elementary) particlesincluding the photons also wave characteristics possess (see also: Wave particle dualism; Quantum electrodynamics).

1 history
2 symbol
3 characteristics
4 reciprocal effect of photons with subject
Literature 6
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since

the antique one there were 5 different, often each other contradicting conceptions over the characteristic of the light. In 19. Century competed waving and particle theories. During many phenomena such as interference - and polarization features for oneIt also indications for a particle character spoke, gave Wellennatur of the light. A historically very important experiment, which referred to a particle nature of the light, was in the year 1887 the observation of the photoelectric effect by Heinrich Hertz and Wilhelm resounding wax.

ThoseQuantization of the electromagnetic radiation goes finally on the explanation of the black body radiation through Max Planck in the year 1900 back (Planck' sches radiation law). Planck placed itself however not the electromagnetic radiation actually quantized forwards, but explained quantization thereby,that the oscillators in the walls of the black body resonators only discrete energy quantities with the electromagnetic field to exchange can.

Albert Einstein described 1905 in his publication to the photoelectric effect the light as from light quanta with particle characteristics existing (for this work it became 1921 with the Nobelpreis excellently). The formal quantum theory of the light was only developed since 1925 beginning with work by max fount , Pascual Jordan and Werner Heisenberg. To today valid theory of the electromagnetic radiation, whatever describes the light quanta,quantum electrodynamics (QED), decreases/goes back in its beginnings to a work of Paul Dirac in the year 1927, in which it describes the reciprocal effect of quantized electromagnetic radiation with an atom. The QED was developed into the 1940er years and 1965with the award of the Nobelpreises for physics at smelling pool of broadcasting corporations P. Feynman, Julian oscillator and Shinichiro Tomonaga appreciative.

The term photon was coined/shaped 1926 by the chemist Gilbert Newton Lewis, which did not understand by it however the light quantum. It used thatTerm in the context (and generally did not recognize) of a model of the reciprocal effect of atoms with light, suggested by him.

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symbol

for the photon becomes generally the symbol <math> \ gamma< /math> (gamma) uses. In high-energy physics is thisSymbol however reserved for the high-energy photons of the gamma radiation (gamma quanta), and the Roentgen photons likewise relevant in this branch of physics receive the symbol X (from English: X-ray).

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characteristics

any electromagnetic radiation, from Radiowellen to the gamma radiation, is quantized in photons. That means, the smallest quantity of electromagnetic radiation of arbitrary frequency is a photon. Photons have an infinite natural life span, can however with a multiplicity of physical processes be produced or destroyed. Photons probably possess no proper mass. The experimentally determined and accepted upper barrier is to 17 <}> ~eV /math with math 6 \ cdot 10^ {<-> (Source:Particle DATA Group). A free photon never is in peace, but moves with the vacuum speed of light. In optical media the effective speed of light is due tothe reciprocal effect of the photons with the subject reduces. Since photons possess energy, they interact in accordance with general relativity theory with the gravitation.

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production and detection

photons can be produced in various kinds, in particular by transitions (“quantum transitions“) of electrons between different conditions (z. B. different atomic or molecule orbital or bands in a solid body). Photons can be produced also with nuclear transitions, particle antiparticle - destruction reactions, or by arbitrary fluctuations in an electromagnetic field.

To the proofof photon fluxes z can. B.Photomultiplier, photoconductor or photodiodes to be used. CCDs, Vidicon, PSDs, Quadrantendioden or Fotoplatten and - films for localsolvent detection by photons are used. In the IR - Range also bolometers are used. Photons within the gamma-ray rangecan be proven by Geiger counters individually. Photomultipliers and Avalanche photodiodes can be used also for single photon detection within the optical range, whereby photomultipliers possess generally the lower dark counting rate, Avalanche photodiodes however still with lower photon energies into the IR range are applicable.

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Spin

photons are spin -1 particles and thus bosons. Thus as many as desired photons the same quantum-mechanical condition can occupy, which is realized for example in a laser. Photons obtain the electromagnetic reciprocal effect: They are the particles, itpermit other particles to change-work with one another electromagnetically. Since the electromagnetic reciprocal effect is a so-called gauge theory, the photons rank among the calibration bosons.

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photons in the vacuum

in the vacuum move photons with the vacuum speed of light <math> C \,< /math> = 299792458 ms⁻¹. The Dispersionsrelation, i.e. the dependence of the energy <math> W \,< /math> of the frequency <math> \ nu \,< /math> (ny), is linear, and the proportionality constant is that Planck' sche quantum of action <math> h \,< /math>,

< math> W=pc=h \ nu \. </math>

The impulse <math> p \,< /math> a photon amounts to thereby

< math> p= \ frac {h \ nu} {C} = \ frac {h} {\ lambda} \. </math>

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photonsin media

in a material photons interact to surrounding medium with that it, from which changed characteristics result. The photon can be absorbed, whereby its energy does not disappear naturally, but into elementary suggestions (quasi-particles) of the medium such as phonons or Exzitonen turns into. Possible it is also that it spreads by a medium; for example as coupled pair of phonon photons (pole air clay/tone). These elementary suggestions in subject have usually no linear Dispersionsrelation, and its propagation speed is lower than the vacuum speed of light untiltoo only unite meters per second for special materials.

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reciprocal effect of photons with subject

photons on subject release with certain energies different processes meet. Within the range of:

1 eV-100 keV photoelectric effect,
100 keV-1 MeV Compton-effect,
1.022 MeV-6 MeV pair creation
2.18 MeV-16 MeV core photo effect.

These effects contribute considerably to the fact that one can detect this radiation and determined itself materials with certain effects on the basis the gamma spectroscopy prove to let.

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