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In physics, scattering is a class of phenomena by which particles are deflected by collisions with other particles.
In astronomy and optics
scattering is deflection of photons that by macroscopic surfaces such
as an asteroid or by small particles as in the rings of Saturn. No atomic or molecular absorption or emission processes are involved. The sky is blue because molecules in the air preferentially scatter blue light.
Rayleigh and Mie scattering
Scattering, also called scatter, is the process by which small particles suspended in a medium of a different index of
refraction diffuse a portion of the incident radiation in all directions. In scattering, no energy transformation results, only a
change in the spatial distribution of the radiation.
Along with absorption, scattering is a major cause of the attenuation of radiation by the atmosphere. Scattering varies as a function of the ratio of the particle diameter to the
wavelength of the radiation. When this ratio is less than about one-tenth, Rayleigh scattering occurs in which the scattering coefficient varies inversely as the fourth power of
the wavelength. At larger values of the ratio of particle diameter to wavelength, the scattering varies in a complex fashion
described by the Mie theory; at a ratio of the order of 10, the laws of
geometric optics begin to apply.
Scattering in particle physics
In particle physics, scattering refers to
deflection of subatomic particles, a process central to many
experiments. In scattering experiments, a target of some material is bombarded with a beam of particles (typically electrons, protons, or neutrons) and the number of particles emerging in various directions is measured. This distribution reveals
information about the interaction that takes place between the target and the scattered particle.
A famous scattering experiment of alpha particles off gold nuclei performed by Ernest
Rutherford revealed the basic structure of the atom - a tiny nucleus surrounded by electrons. See Rutherford scattering. Scattering has also been done off of
nucleons and quarks.
Mathematically, scientists describe scattering by an impact parameter (which describes how close the incident particle would
come to the target if it moved in a straight line) and an angle of deflection (which describes the angle at which the particle
emerges relative to its original direction). The distribution of deflection angles is described by a function known as the
differential cross section, which (roughly) relates a direction in space in which some particles emerge to the amount of the
incoming beam (in area) those particles came from.
The abstract mathematics of scattering is developed as scattering theory.
See also:
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