Définition de mot-cléf
Electromagnetic radiation is a ubiquitous phenomenon that takes the form of self-propagating waves in a vacuum or in matter. It consists of electric and magnetic field components which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation. Electromagnetic radiation is classified into several types according to the frequency of its wave; these types include (in order of increasing frequency and decreasing wavelength): radio waves, microwaves, terahertz radiation, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. A small and somewhat variable window of frequencies is sensed by the eyes of various organisms; this is what we call the visible spectrum, or light. (excerpted from “electromagnetic radiation”, Wikipedia, Sept 16th, 2009).
Electromagnetic radiation interacts with matter in different ways in different parts of the spectrum. The types of interaction can be so different that it seems to be justified to refer to different types of radiation. At the same time there is a continuum containing all these "different kinds" of electromagnetic radiation. Thus we refer to a spectrum, but divide it up based on the different interactions with matter.
|Region of the spectrum||Main interactions with matter|
|Radio||Collective oscillation of charge carriers in bulk material (plasma oscillation). An example would be the oscillation of the electrons in an antenna.|
|Microwave through far infrared||Plasma oscillation, molecular rotation|
|Near infrared||Molecular vibration, plasma oscillation (in metals only)|
|Visible||Molecular electron excitation (including pigment molecules found in the human retina), plasma oscillations (in metals only)|
|Ultraviolet||Excitation of molecular and atomic valence electrons, including ejection of the electrons (photoelectric effect)|
|X-rays||Excitation and ejection of core atomic electrons|
|Gamma rays||Energetic ejection of core electrons in heavy elements, excitation of atomic nuclei, including dissociation of nuclei|
|High energy gamma rays||Creation of particle-antiparticle pairs. At very high energies a single photon can create a shower of high energy particles and antiparticles upon interaction with matter.|
(excerpted from “electromagnetic spectrum”, Wikipedia, Sept 16th, 2009).
Catégorie: Techniques analytiques
Les mots-clés tel que “AAS”, “FA-NA”. On les retrouve dans le tableau “Analytical_Techniques_SHARED”.
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