Interaction radiation-matter

The interactions radiation-matter describe the effects of a radiation on a Atome. The term “radiation” is to be taken in its quantum direction :

electromagnetic Radiation (Light, X-ray, Gamma ray);
particle (electron, Neutron, Radiation alpha).

These radiations are used to analyze the matter. Indeed, the atoms are too small to be visible or palpable, one can thus know them only in an indirect way; one looks at the way in which they disturb an incidental radiation. This gave rise to two types of methods of analysis:

methods of Diffraction: when the atoms are organized in an ordered way (Cristal), the radiation will be diffused in certain directions of space only; the study of this space distribution of the diffused intensity makes it possible to characterize the organization of the matter;
the spectrometric methods : the atoms will absorb part of incidental radiations and will re-emit others of them, the réémission and absorption spectrum is characteristic of its chemical nature and binding energies of the matter, thus.

Diffusion, ionization

The incidental radiation can interact several manners with the atom:

it can be diffused, i.e. it “rebounds” on the atom:

elastic scattering: the radiation rebounds without losing energy; if the incidental radiation is electromagnetic (light, x-ray) one speaks about Diffusion Rayleigh, if it is an electron, one speaks about retrodiffusion;
inelastic scattering: the radiation causes the ejection of a slightly bound electron, it thus loses energy, it is the diffusion Compton;

it can be absorbed, by causing an electronic transition:

if incidental energy is weak, it causes simply the change of orbit of an electron;
if energy is sufficient, it causes an ionization; if the incidental radiation is electromagnetic, one speaks about photoelectric Effet and the ejected electron is a photoelectron; if the incidental radiation is an electron beam, the ejected electrons are secondary electrons.

Relieving

In the case or the radiation is absorbed, the atom is known as “excited” because its state of energy is not the minimal state. It thus follows a “relieving” (or “de-energizing”): an electron of a roadbase comes to fill the vacant quantum box left by the ejected electron.

If energy of transition is moderate (i.e. if the incidental radiation had a moderate energy), relieving causes the emission of a photon of weak energy (visible or ultraviolet), it is the phenomenon of Fluorescence. If the energy of transition is raised, one can have two cases:

there is emission of a fluorescent photon, which because of its energy, is a photon X, one speaks about x-ray fluorescence;
this photon X can be recaptured by the atom itself and to cause the ejection of an outer-shell electron, it is the emission Auger.

Another interactions

Spin, electronic paramagnetic Resonance, nuclear Magnetic resonance and Medical imagery
Phonon, Raman Spectrometry

Applications

External bonds

Interactions electrons/matter, laboratory of materials, Catholic school of arts and trades.

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