Fr.: diffusion résonante
The absorption and prompt re-emission of photons of a particular wavelength by an atom. In this process, a photon of exactly the right wavelength (i.e. energy) excites an electron in the atom from one energy level to another. The electron then drops back down to its original energy level more or less immediately, emitting a photon of almost identical energy to the one that was absorbed in the first place, but in some random direction. Resonant scattering applies only to line radiation, unlike other forms of scattering which are of continuous radiation (Oxford Dictionary of Astronomy, 2 ed.).
The process in which the direction of motion of → particles
or → waves is changed randomly because of their
→ interactions (→ collisions)
with other particles of the → medium transversed.
Verbal noun of → scatter.
Fr.: angle de diffusion
The angle between the → incident radiation on a → particle (such as a water droplet in a rainbow) and the scattered radiation (such as the light ray leaving the droplet). Scattering angle is a function of → impact parameter. In other words, The angle along which the change of direction has taken place, irrespective whether radiation is scattered by particles or reflected (refracted) by a surface.
Fr.: coefficient de diffusion
The fraction of light scattered per unit distance in a medium.
scattering of stars
Fr.: diffusion des étoiles
The progressive increase of random motions of → disk stars with increasing stellar → ages. While some initial random motion seems likely in the disturbed conditions of disks when the oldest stars formed, the observation is generally attributed to scattering processes. Both massive gas → clumps and → spiral waves are considered as scattering agents (J. A. Sellwood & J. J. Binney, 2002, astro-ph/0203510 and references therein).
Fr.: diffusion sélective
Fr.: diffusion unique, ~ simple
A type of scattering where photons are scattered only once. Single scattering dominates in → optically thin media, since photons have a high probability of exiting the medium (e.g., a thin cloud) before being scattered again.
parâkaneš bâ vâruni-ye espin
Fr.: diffusion avec renversement du spin
Quantum mechanics: The scattering of a particle that reverses the spin direction.
surface of last scattering
ruye-ye vâpasin parâkaneš
Fr.: surface de dernière diffusion
Same as → last scattering surface.
parâkaneš-e Thomson (#)
Fr.: diffusion de Thomson
The classical, → non-relativistic scattering of photons by free charged particles. When an electromagnetic wave is incident on a charged particle, the electric and magnetic components of the wave exert a force on the particle, setting it into motion. As it accelerates, it in turn radiates in all directions. Such scattering is independent of wavelength and equal numbers of photons are scattered forward and backward. Thomson scattering occurs in stellar atmospheres and in any non-relativistic → plasma. Thomson scattering is normally taken as the minimum → opacity.