View source for Proton

{{Infobox Particle
| bgcolour =
| classification = [[Baryon]]
| name = Proton
| image = [[Image:Quark structure proton.svg|250px]]
| caption = The quark structure of the proton.
| num_types = 
| composition = 2 up, 1 down
| family = [[Fermion]]
| group = [[Quark]]
| generation =
| interaction = [[Gravity]], [[Electromagnetic interaction|Electromagnetic]], [[Weak interaction|Weak]], [[Strong interaction|Strong]]
| antiparticle = [[Antiproton]]
| theorized = [[William Prout]] (1815)
| discovered = [[Ernest Rutherford]] (1919)
| symbol = {{SubatomicParticle|Proton}}, {{SubatomicParticle|Proton+}}, {{SubatomicParticle|Nucleon+}}
| mass = 1.6726×10^−27 kg
{{val|938.272029|(80)|u=MeV/c2}}
{{val|1.00727646688|(13)|u=u}} 
| mean_lifetime = >{{val|1.9||e=29|u=years}} (stable)
| electric_charge = 1.60217653(14)×10^−19 C
| charge_radius = 0.875(7) fm
| electric_dipole_moment = <{{val|5.4||e=-24|u=e cm}}
| electric_polarizability = {{val|1.20|(6)|e=-3|u=fm<sup>3</sup>}}
| magnetic_moment = 2.792847351(28) [[Nuclear magneton|μ<sub>N</sub>]]
| magnetic_polarizability = {{val|1.9|(5)|e=-4|u=fm<sup>3</sup>}}
| spin = ½
| isospin = ½
| parity = +1
| condensed_symmetries = I(J<sup>P</sup>) = ½(½<sup>+</sup>)
}}
{{EH}}

In [[physics]], the '''proton''' ([[Greek language|Greek]] ''πρώτον'' / ''proton'' = first) is a [[subatomic particle]] with an [[electric charge]] of one positive [[elementary charge|fundamental unit]] 1.60217653(14)×10^−19 C, a diameter of about 1.65x10^-15 m <ref>{{cite web |url=http://scienceworld.wolfram.com/physics/Proton.html |title=Proton—from Eric Weisstein's World of Physics |first=Eric |last=Weisstein |publisher=Wolfram Research, Inc. |date=1996–2007 |accessdate=2007-01-16}}</ref>, and a mass of (938.27231 MeV/c2) (1.00727646688(13) u), (1.6726x10^-27 kg), or about 1836 times the mass of an [[electron]].

==History==
[[Ernest Rutherford]] is generally credited with the discovery of the proton. In 1918 Rutherford noticed that when alpha particles were shot into nitrogen gas, his [[scintillation detector]]s showed the signatures of hydrogen nuclei. Rutherford determined that the only place this hydrogen could have come from was the nitrogen, and therefore nitrogen must contain hydrogen nuclei. He thus suggested that the hydrogen nucleus, which was known to have an [[atomic number]] of 1, was an [[elementary particle]].
{{seealso|William Prout|Prout's hypothesis}}

Prior to Rutherford, [[Eugene Goldstein]] had observed [[canal rays]], which were composed of positively charged [[ion]]s. After the discovery of the [[electron]] by [[J.J. Thomson]], Goldstein suggested that since the atom is electrically neutral there must be a positively charged particle in the atom and tried to discover it. He used the "canal rays" observed to be moving against the electron flow in [[cathode ray tubes]]. After the electron had been removed from particles inside the cathode ray tube they became positively charged and moved towards the cathode. Most of the charged particles passed through the cathode, it being perforated, and produced a glow on the glass. At this point, Goldstein believed that he had discovered the proton.<ref>Gilreath, Esmarch S.: "Fundamental Concepts of Inorganic Chemistry.", page 5. New York: McGraw–Hill, 1958.</ref> When he calculated the ratio of charge to mass of this new particle (which in case of the electron was found to be the same for every gas that was used in the cathode ray tube) was found to be different when the gases used were changed. The reason was simple. What Goldstein assumed to be a proton was actually an ion. He gave up his work there, but promised that "he would return." However, he was widely ignored.

==Description==
Protons are [[spin (physics)|spin]] &minus;1/2 [[fermion]]s and are composed of three [[quark]]s<ref>Adair, Robert K.: "The Great Design: Particles, Fields, and Creation.", page 214. New York: Oxford University Press, 1989.</ref>, making them [[baryon]]s. The two [[up quark]]s and one [[down quark]] of the proton are held together by the [[strong interaction|strong force]], mediated by [[gluon]]s.

Protons and [[neutron]]s are both [[nucleons]], which may be bound by the [[nuclear force]] into [[atomic nucleus|atomic nuclei]]. The nucleus of the most common [[isotope]] of the [[hydrogen]] [[atom]] is a single proton (it contains no neutrons). The nuclei of heavy hydrogen ([[deuterium]] and [[tritium]]) contain neutrons. All other types atoms are composed of two or more protons and various numbers of neutrons. The number of protons in the nucleus determines the chemical properties of the atom and thus which [[chemical element]] is represented; it is the number of both neutrons and protons in a [[nuclide]] which determine the particular [[isotope]] of an element.

==Antiproton==
{{main|antiproton}}
The [[antiparticle]] of the proton is the '''antiproton'''. It was discovered in 1955 by [[Emilio Segrè]] and [[Owen Chamberlain]], for which they were awarded the 1959 [[Nobel Prize in Physics]].

[[CPT-symmetry]] puts strong constraints on the relative properties of particles and [[antiparticles]] and, therefore, is open to stringent tests. For example, the charges of the proton and antiproton must sum to exactly zero. This equality has been tested to one part in 10^8. The equality of their masses is also tested to better than one part in 10^8. By holding antiprotons in a [[Penning trap]], the equality of the charge to mass ratio of the proton and the antiproton has been tested to 1 part in 9 x 10^11. The [[magnetic moment]] of the antiproton has been measured with error of 8 x 10^-3 nuclear [[Bohr magneton]]s, and is found to be equal and opposite to that of the proton.

==High-energy physics==
Due to their stability and large mass (relative to [[electron]]s), protons are well suited to use in [[particle collider]]s such as the [[Large Hadron Collider]] at [[CERN]] and the [[Tevatron]] at [[Fermilab]]. Protons also make up a large majority of the [[cosmic ray]]s which impinge on the [[Earth's atmosphere]]. Such high-energy proton collisions are more complicated to study than electron collisions, due to the composite nature of the proton. Understanding the details of proton structure requires [[quantum chromodynamics]].

==See also==
<div style="-moz-column-count:2; column-count:2;">
*[[particle physics]]
*[[subatomic particle]]
*[[quark model]]
*[[neutron]]
*[[electron]]
*[[proton-proton chain reaction]]
*[[proton pump]]
*[[proton pump inhibitor]]
*[[proton therapy]]
*[[list of particles]]
*[[fermion field]]
*[[proton decay]]
</div>

==References==

{{reflist|2}}

==External links==
{{commons}}
* [http://pdg.lbl.gov Particle Data Group]
* [http://www.cern.ch/lhc/ Large Hadron Collider]

{{particles}}

[[Category:Nucleons]]
[[Category:Hydrogen physics]]
[[Category:Fundamental physics concepts]]

{{Link FA|lmo}}

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[[ar:بروتون]]
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[[bn:প্রোটন]]
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[[be-x-old:Пратон]]
[[bs:Proton]]
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[[bg:Протон]]
[[ca:Protó]]
[[cv:Протон]]
[[cs:Proton]]
[[cy:Proton]]
[[da:Proton]]
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[[el:Πρωτόνιο]]
[[es:Protón]]
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[[eu:Protoi]]
[[fa:پروتون]]
[[fr:Proton]]
[[ga:Prótón]]
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[[zh-classical:質子]]
[[ko:양성자]]
[[hi:प्रोटॉन]]
[[hr:Proton]]
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[[is:Róteind]]
[[it:Protone]]
[[he:פרוטון]]
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[[sw:Protoni]]
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[[ms:Proton]]
[[mn:Протон]]
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[[ja:陽子]]
[[no:Proton]]
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[[nov:Protone]]
[[oc:Proton]]
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[[pt:Próton]]
[[ksh:Proton]]
[[ro:Proton]]
[[qu:Prutun]]
[[ru:Протон]]
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[[scn:Prutoni]]
[[simple:Proton]]
[[sk:Protón]]
[[sl:Proton]]
[[sr:Протон]]
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[[stq:Proton]]
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[[fi:Protoni]]
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[[ta:நேர்மின்னி]]
[[th:โปรตอน]]
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[[tr:Proton]]
[[uk:Протон]]
[[ur:اولیہ (جوہر)]]
[[vec:Proton]]
[[yo:Àkọ́wá]]
[[bat-smg:Pruotuons]]
[[zh:質子]]

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