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Longman Dictionary of Contemporary English
▪ Assignments of exchangeable protons are shown.
▪ At this point it must seem paradoxical that atomic nuclei containing several closely packed protons exist at all.
▪ Is his identity dependent upon the particular choice of electrons, protons, and other particles that compose those atoms?
▪ Quarks are thought to be the fundamental particles from which matter, such as protons, is built.
▪ The mass of the proton is 1836 times that of an electron, yet their electrical charges equate.
▪ The nucleus has two protons and two neutrons.
▪ The number of protons remains the same, even though electrons may be lost or gained.
▪ This incredibly dense, hot soup of protons and electrons is called fluid metallic hydrogen.
Douglas Harper's Etymology Dictionary

1920 in physics, coined by English physicist Ernest Rutherford (1871-1937) from noun use of Greek proton, neuter of protos "first" (see proto-), on analogy of electron; supposedly because hydrogen was hypothesized as a constituent of all the elements. The word was used earlier in embryology (1893) as a translation of German anlage ("fundamental thing") based on Aristotle's phrase he prote ousia to proton.


n. (context particle English) positively charged subatomic particle forming part of the nucleus of an atom and determining the atomic number of an element; the nucleus of the most common isotope of hydrogen; composed of two up quarks and a down quark


n. a stable particle with positive charge equal to the negative charge of an electron


A proton is a subatomic particle, symbol or , with a positive electric charge of +1e elementary charge and mass slightly less than that of a neutron. Protons and neutrons, each with masses of approximately one atomic mass unit, are collectively referred to as " nucleons". One or more protons are present in the nucleus of every atom. The number of protons in the nucleus is the defining property of an element, and is referred to as the atomic number (represented by the symbol Z). Since each element has a unique number of protons, each element has its own unique atomic number. The word proton is Greek for "first", and this name was given to the hydrogen nucleus by Ernest Rutherford in 1920. In previous years Rutherford had discovered that the hydrogen nucleus (known to be the lightest nucleus) could be extracted from the nuclei of nitrogen by collision. Protons were therefore a candidate to be a fundamental particle and a building block of nitrogen and all other heavier atomic nuclei.

In the modern Standard Model of particle physics, protons are hadrons, and like neutrons, the other nucleon (particle present in atomic nuclei), are composed of three quarks. Although protons were originally considered fundamental or elementary particles, they are now known to be composed of three valence quarks: two up quarks and one down quark. The rest masses of quarks contribute only about 1% of a proton's mass, however. The remainder of a proton's mass is due to quantum chromodynamics binding energy, which includes the kinetic energy of the quarks and the energy of the gluon fields that bind the quarks together. Because protons are not fundamental particles, they possess a physical size, though not a definite one; the root mean square charge radius of a proton is about 0.84–0.87 fm or to .

At sufficiently low temperatures, free protons will bind to electrons. However, the character of such bound protons does not change, and they remain protons. A fast proton moving through matter will slow by interactions with electrons and nuclei, until it is captured by the electron cloud of an atom. The result is a protonated atom, which is a chemical compound of hydrogen. In vacuum, when free electrons are present, a sufficiently slow proton may pick up a single free electron, becoming a neutral hydrogen atom, which is chemically a free radical. Such "free hydrogen atoms" tend to react chemically with many other types of atoms at sufficiently low energies. When free hydrogen atoms react with each other, they form neutral hydrogen molecules (H), which are the most common molecular component of molecular clouds in interstellar space. Such molecules of hydrogen on Earth may then serve (among many other uses) as a convenient source of protons for accelerators (as used in proton therapy) and other hadron particle physics experiments that require protons to accelerate, with the most powerful and noted example being the Large Hadron Collider.

Proton (disambiguation)

A proton is a subatomic particle.

Proton may also refer to:

Proton (supermarkets)

Proton is a Greek based retail chain of independent retailers (primarily grocery shops) operating as a brand and buying group (or symbol group). All stores are independently owned. The parent company (ELETA LTD) is communally owned with each retailer owning a share. As of 2006, the Proton retail network consists of around 390 stores throughout Greece. They also sell their own brand of cola, Proton Cola.

Proton (rocket family)

Proton (Russian: Протон) (formal designation: UR-500) is an expendable launch system used for both commercial and Russian government space launches. The first Proton rocket was launched in 1965. Modern versions of the launch system are still in use as of 2016, making it one of the most successful heavy boosters in the history of spaceflight. All Protons are built at the Khrunichev State Research and Production Space Center plant in Moscow, transported to the Baikonur Cosmodrome, brought to the launch pad horizontally, and raised into vertical position for launch.

As with many Soviet rockets, the names of recurring payloads became associated with the Proton. The moniker "Proton" originates from a series of similarly named scientific satellites, which were among the rocket's first payloads. During the Cold War, it was designated the D-1/D-1e or SL-12/SL-13 by Western intelligence agencies.

Launch capacity to low Earth orbit is about . Geostationary transfer capacity is about . Commercial launches are marketed by International Launch Services (ILS). The rocket is intended to be retired before 2030.

Proton (bank card)

Proton is an electronic purse application for debit cards in Belgium. The system was introduced in February 1995 with the goal to replace cash primarily for small transactions around € 15. For security, the card is limited to storing 125.00 EUR of available electronic cash (originally 5,000 BEF).

The card is used for small payments without a pin code or signature, and runs the same risk as with ordinary cash in that if the card is lost the cash value allocated to the card is also lost.

The advantage to merchants is that they can accept payments without the necessity for a bank terminal to be connected to a centralised system for approving the transaction (the transaction is approved by the card itself), and the transaction is very quick.

Proton has seen limited success in Belgium, despite being available on commonplace on parking meters, pay phones, and within convenience stores; possibly due to a poor understanding of the system. Despite this, the system has also been implemented in other countries such as Chipknip in the Netherlands, and has been considered for other markets such as Australia.

Security was based on the Message authentication code.

The system will be retired on 31 December 2014. Customers are requested to offload the charged amount back onto their bank account before the expiration date.

Usage examples of "proton".

Proton, plus the societies of werewolves, unicorns, vampires, demons and assorted monsters.

But as far back as 1950, hyperons had been discovered, elementary particles bigger than protons and neutrons.

The high-energy proton spectrpmetry clusters flunked out, too, as did the gravimetric distortion mapping scanner, the fixed angle gamma frequency counter, the wide-angle EM radiation imaging scanner, the quark population analysis counter, the Z-range particulate spectrometry sensor, the low-frequency EM flux sensor, the localized subspace field stress sensor, the parametric subspace field stress sensor, the hydrogen-filter subspace flux scanner, the linear calibration subspace flux sensor, the variable band optical imagining cluster, the virtual aperture graviton flux spectrometer, the high-resolution graviton flux spectrometer, the very low energy graviton spin pola-rimeter, the passive imaging gamma interferometry sensor, the low-level imagining sensor, the virtual particle mapping camera, and even the life-form analysis instrument counter.

Anchee Ye and Penn Brown spend a week at the Kennedy Space Center, learning how to use the proton drill rig.

In the first microsecond, space was filled with quagma, a swarming magma of quarks, as if the whole universe was a single huge proton.

Paraetonium to Siwa to here, hundreds of kilometers beyond human thought or action, half a mile down, where the gigantic claw diggers had ceased their abrading, the two of us with simple pick and shovel, standing on the last thin layer of compacted dirt and rock that roofed whatever great shadowy structure lay beneath us, a shadow picked up by the most advanced deep-resonance-response readings, verified on-site by proton free-precession magnetometry and ground-penetrating radar brought in from the Sandia National Laboratory in Albuquerque, New Mexico, in the United States.

Actually, that makes sense: neutrons decaying into protons and pions would transmute some of the calcium to scandium, the oxygen to fluorine, and the carbon to nitrogen.

It was a heavy isotope of hydrogen, with one proton and one neutron, and the Big Bang had made only a pinch of it, before stingily shutting off production just three minutes after creation.

Sam Cottage, monitoring the Sun on the morning after lift-off, saw with interest that Region 419 had maintained its horseshoe configuration, with signs indicating that a sunspot big enough to see with the naked eye might be developing, but there was no indication that a solar proton event might erupt.

ATP synthase molecule as the protons pass through a tunnel and out the other side of the membrane.

She got one in her sights and used a proton torpedo while it still made sense, then needled it with laserfire until the torp got there and blew it into molten slag.

Two twistor combinations produce electrons, three can create protons and neutrons, die building blocks of atomic nuclei.

He soon found that if beryllium was bombarded with alpha particles, a kind of radiation consisting of particles with a mass close to that of the proton were produced.

When protons were bombarded with high-energy electrons, pointlike charges were discovered inside the proton.

The more typical vibrating fundamental string corresponds to a particle whose mass is billions upon billions times greater than that of the proton.