Editing Scattering (section)

{{Short description|Range of physical processes}}
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{{Scattering}}
[[File:Wine glass in LCD projectors beam.jpg|thumb|[[Wine glass]] in [[LCD projector]]s light beam makes the beam scatter.]]
In physics, '''scattering''' is a wide range of physical processes where moving particles or radiation of some form, such as [[light]] or [[sound]], are forced to deviate from a straight [[trajectory]] by localized non-uniformities (including particles and radiation) in the medium through which they pass. In conventional use, this also includes deviation of reflected radiation from the angle predicted by the [[law of reflection]]. Reflections of radiation that undergo scattering are often called ''[[diffuse reflection]]s'' and unscattered reflections are called ''[[specular]]'' (mirror-like) reflections. Originally, the term was confined to light scattering (going back at least as far as [[Isaac Newton]] in the 17th century<ref>{{cite journal |last1=Newton |first1=Isaac |title=A letter of Mr. Isaac Newton Containing his New Theory About Light and Colours |journal=Philosophical Transactions |date=1665 |volume=6 |page=3087 |publisher=Royal Society of London}}</ref>). As more "ray"-like phenomena were discovered, the idea of scattering was extended to them, so that [[William Herschel]] could refer to the scattering of "heat rays" (not then recognized as electromagnetic in nature) in 1800.<ref>{{cite journal |last1=Herschel |first1=William |title=Experiments on the Solar, and on the Terrestrial Rays that Occasion Heat |journal=Philosophical Transactions |date=1800 |volume=XC |page=770 |publisher=Royal Society of London}}</ref> [[John Tyndall]], a pioneer in light scattering research, noted the connection between light scattering and acoustic scattering in the 1870s.<ref>{{cite journal |last1=Tyndall |first1=John |title=On the Atmosphere as a Vehicle of Sound |journal=Philosophical Transactions of the Royal Society of London |date=1874 |volume=164 |page=221 |jstor=109101 |bibcode=1874RSPT..164..183T |url=https://www.jstor.org/stable/109101}}</ref> Near the end of the 19th century, the scattering of [[cathode ray]]s (electron beams)<ref>{{cite journal |last1=Merritt |first1=Ernest |title=The Magnetic Deflection of Diffusely Reflected Cathode Rays |journal=Electrical Review |date=5 Oct 1898 |volume=33 |issue=14 |page=217 |url=https://books.google.com/books?id=j0Q_AQAAMAAJ&pg=PA217}}</ref> and X-rays<ref>{{cite journal |title=Recent Work with Röntgen Rays |journal=Nature |date=30 Apr 1896 |volume=53 |issue=1383 |pages=613–616 |doi=10.1038/053613a0 |bibcode=1896Natur..53..613. |s2cid=4023635 |url=https://books.google.com/books?id=X-CiNgBQgR4C&pg=PA615|doi-access=free }}</ref> was observed and discussed. With the discovery of subatomic particles (e.g. [[Ernest Rutherford]] in 1911<ref>{{cite journal|first=E. |last=Rutherford |author-link=Ernest Rutherford |title=The Scattering of α and β rays by Matter and the Structure of the Atom |journal=Philosophical Magazine |volume=6 |page=21 |date=1911}}</ref>) and the development of quantum theory in the 20th century, the sense of the term became broader as it was recognized that the same mathematical frameworks used in light scattering could be applied to many other phenomena.

Scattering can refer to the consequences of [[particle collision|particle-particle collisions]] between molecules, atoms, [[electron]]s, photons and other particles. Examples include: [[cosmic ray]] scattering in the Earth's upper atmosphere; particle collisions inside [[particle accelerator]]s; electron scattering by gas atoms in fluorescent lamps; and [[neutron scattering]] inside [[nuclear reactor]]s.<ref>[[John H. Seinfeld|Seinfeld]], John H.; Pandis, Spyros N. (2006). Atmospheric Chemistry and Physics - From Air Pollution to Climate Change (2nd Ed.). John Wiley and Sons, Inc. {{ISBN|0-471-82857-2}}</ref>

The types of non-uniformities which can cause scattering, sometimes known as ''scatterers'' or ''scattering centers'', are too numerous to list, but a small sample includes [[particle]]s, [[Liquid bubble|bubble]]s, [[droplet]]s, [[density]] fluctuations in [[fluid]]s, [[crystallite]]s in [[polycrystal]]line solids, defects in [[monocrystal]]line solids, [[surface roughness]], [[cell (biology)|cell]]s in organisms, and textile [[fiber]]s in clothing. The effects of such features on the path of almost any type of propagating wave or moving particle can be described in the framework of [[scattering theory]].

Some areas where scattering and scattering theory are significant include radar sensing, [[medical ultrasound]], [[semiconductor wafer]] inspection, [[polymerization]] process monitoring, acoustic tiling, free-space communications and [[computer-generated imagery]].<ref>{{cite book |last= Colton |first= David|author2=Rainer Kress  |title= Inverse Acoustic and Electromagnetic Scattering Theory |publisher= [[Springer Science+Business Media|Springer]] |year= 1998 |isbn= 978-3-540-62838-5 }}</ref> Particle-particle scattering theory is important in areas such as [[particle physics]], [[atomic, molecular, and optical physics]], [[nuclear physics]] and [[astrophysics]]. In particle physics the quantum interaction and scattering of fundamental particles is described by the Scattering Matrix or [[S-Matrix]], introduced and developed by [[John Archibald Wheeler]] and [[Werner Heisenberg]].<ref>{{cite book |last1=Nachtmann |first1=Otto |title=Elementary Particle Physics: Concepts and Phenomena |publisher=Springer-Verlag |date=1990 |pages=80–93 |isbn=3-540-50496-6 }}</ref>

Scattering is quantified using many different concepts, including [[Cross section (physics)|scattering cross section]] (σ), [[attenuation coefficient]]s, the [[bidirectional scattering distribution function]] (BSDF), [[S-matrix|S-matrices]], and [[mean free path]].