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proton

proton, elementary particle having a single positive electrical charge and constituting the nucleus of the ordinary hydrogen atom. The positive charge of the nucleus of any atom is due to its protons. Every atomic nucleus contains one or more protons; the number of protons, called the atomic number, is different for every element (see periodic table). The mass of the proton is about 1,840 times the mass of the electron and slightly less than the mass of the neutron. The total number of nucleons, as protons and neutrons are collectively called, in any nucleus is the mass number of the nucleus. The existence of the nucleus was postulated by Ernest Rutherford in 1911 to explain his experiments on the scattering of alpha particles; in 1919 he discovered the proton as a product of the disintegration of the atomic nucleus. The proton and the neutron are regarded as two aspects or states of a single entity, the nucleon. The proton is the lightest of the baryon class of elementary particles. The proton and other baryons are composed of triplets of the elementary particle called the quark. A proton, for instance, consists of two quarks called up and one quark called down, a neutron consists of two down quarks and an up quark. The antiparticle of the proton, the antiproton, was discovered in 1955; it has the same mass as the proton but a unit negative charge and opposite magnetic moment. Protons are frequently used in a particle accelerator as either the bombarding (accelerated) particle, the target nucleus, or both. The possibility that the proton may have a finite lifetime has recently come under examination. If the proton does indeed decay into lighter products, however, it takes an extremely long time to do so; experimental evidence suggests that the proton has a lifetime of at least 1031 years.

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proton

proton (symbol p) Stable elementary particle with a positive charge equal in magnitude to the negative charge of the electron. The proton was discovered (1919) by Ernest Rutherford. It forms the nucleus of the lightest isotope of hydrogen and, with the neutron, is a constituent of the nuclei of all other elements. It is made up of three quarks. The proton is a baryon with a mass c.1836 times heavier than the electron. The number of protons in the nucleus of an element is equal to its atomic number. Protons also occur in primary cosmic radiation. Beams of high-velocity protons, produced by particle accelerator, are used to study nuclear reactions. See also particle physics

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proton

pro·ton / ˈprōˌtän/ • n. Physics a stable subatomic particle occurring in all atomic nuclei, with a positive electric charge equal in magnitude to that of an electron, but of opposite sign. DERIVATIVES: pro·ton·ic / prōˈtänik/ adj.

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proton

proton (phys.) unit of matter associated with a charge of positive electricity. XX. — n. sg. of Gr. prôtos first.

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proton

protonAgamemnon, Memnon •ninon, xenon •noumenon • Trianon • xoanon •organon • Simenon • Maintenon •crampon, kampong, tampon •Nippon • coupon •Akron, Dacron, macron •electron • natron • Hebron • positron •Heilbronn • micron •boron, moron, oxymoron •neutron • interferon •fleuron, Huron, neuron •Oberon • mellotron • aileron •cyclotron • Percheron • Mitterrand •vigneron • croissant • Maupassant •garçon • Cartier-Bresson • exon •frisson • Oxon • chanson • Tucson •soupçon • Aubusson • Besançon •penchant • torchon • cabochon •Anton, canton, Danton •lepton •piton, Teton •krypton • feuilleton • magneton •chiton •photon, proton •croûton, futon •eschaton • peloton • contretemps •telethon •talkathon, walkathon •Avon • tableau vivant • vol-au-vent

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Proton

Proton

History and discovery

Properties

Inner structure

Resources

The proton is a positively charged subatomic particle. Protons are one of the fundamental constituents of all atoms. Protons, in addition to neutrons, are found in a very concentrated region of space within atoms referred to as the nucleus. The discovery of the proton, neutron, and electron revolutionized the way scientists viewed the atom. Recent research has shown that protons are themselves made up of even smaller particles called quarks and gluons.

History and discovery

Early atomic theory assumed that atoms were indivisible. However, when English physicist and chemist Michael Faraday (17911867) demonstrated, in 1834, that chemical elements were electrical in nature, scientists embarked on a series of experiments that challenged, and eventually demolished, the fundamental assumptions of traditional atomic theory. For example, in 1878, British chemist and physicist Sir William Crookes (18321919), who predicted the discovery of isotopes, started experimenting with cathode rays, which occurred when electricity was discharged between two metal plates in a tube (later named a Crookes tube) with gas at an extremely low pressure. Crookes believed these rays were negatively charged electrons. In 1897, however, English physicist J. J. Thomson (18561940) identified them as subatomic particles, eventually named electrons. Further experiments led to the discovery of protons. For example, when scientists drilled holes in the positively charged (anode) plate of the Crookes tube, they detected rays moving in the opposite direction (from the anode to the negatively charged cathode) of the cathode rays. Named canal rays, these rays were studied by German physicist Wilhelm Wien (1864 1928). In 1905, Wien identified some of these rays are hydrogen ions. Researchers later established that rays with the least mass were protons.

In 1909, New Zealand-British physicist Ernest Rutherford (18711937) instructed his younger colleague German nuclear physicist Hans Geiger (1882 1945) and German physicist and inventor Ernst Marsden (18891970), who was still an undergraduate, to perform the gold foil experiment. The experimenters bombarded a thin gold foil with alpha particles (helium atoms without electrons). Since the current model of the atom was a positively charged sphere (pudding) with negative globs (plums) inserted throughout (the plum pudding model), they expected the alpha particles to penetrate the foil without resistance. Indeed, most of the alpha particles did, but a small number were strongly repelled. These results indicated that the gold atom had a positively charged nucleus. In 1919, Rutherford identified the proton as the fundamental unit of positive electrical charge in the atom. The neutron, the major particle constituting the atoms nucleus

KEY TERMS

Atomic number The number of protons in the nucleus of an atom.

Gluons Subatomic particles that help to keep quarks bound together.

Quarks Believed to be the most fundamental units of protons and neutrons.

Radioactivity Spontaneous release of subatomic particles or gamma rays by unstable atoms as their nuclei decay.

was discovered in 1932 by English physicist James Chadwick (18911974). Approximately equal to a proton in mass, the neutron has no charge.

Properties

The protons mass and charge have both been determined. The mass is 1.673 x 10-24 g. The charge of a proton is positive, and is assigned a value of +1. The electron has a -1 charge, and is about 2,000 times lighter than a proton. In neutral atoms, the number of protons and electrons are equal.

The number of protons (also referred to as the atomic number) determines the chemical identity of an atom. Each element in the periodic table has a unique number of protons in its nucleus. The chemical behavior of individual elements largely depends, however, on the electrons in that element. Chemical reactions involve changes in the arrangements of electrons, not in the number of protons or neutrons.

The processes involving changes in the number of protons are referred to as nuclear reactions. In essence, a nuclear reaction is the transformation of one element into another. Certain elementsboth natural and artificially madeare by their nature unstable, and spontaneously break down into lighter elements, releasing energy in the process. This process is referred to as radioactivity. Nuclear power is generated by just such a process.

Inner structure

Research has shown the proton to be made up of even smaller constituent particles. A proton is found to consist of two up quarks, each with a +2/3 electric charge, and one down quark, with a -1/3 electric charge. The individual quarks are held together by particles called gluons. The up and down quarks are currently believed to be two of the three fundamental particles of all matter. Recent research has revealed the possibility of an even deeper substructure, and further work could lead to new theories that may overturn the current model of the protons structure. Scientists are continuing to use high-energy beams from within particle accelerators to discover more complex information about protons.

See also Subatomic particles.

Resources

BOOKS

Blaschke, D., M.A. Ivanov, and T. Mannel, eds. Heavy Quark Physics. Berlin, Germany: Springer, 2004.

Folan, Lorcan M. Modern Physics and Technology for Undergraduates. River Edge, NJ: World Scientific, 2003.

Staley, Kent W. The Evidence for the Top Quark: Objectivity and Bias in Collaborative Experimentation. Cambridge, UK, and New York: Cambridge University Press, 2004.

Taylor, John Robert. Modern Physics for Scientists and Engineers. Upper Saddle River, NJ: Pearson Prentice Hall, 2004.

Young, Hugh D. Sears and Zemanskys University Physics. San Francisco, CA: Pearson Addison Wesley, 2004.

Michael G. Roepel

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Proton

Proton

The proton is a positively charged subatomic particle. Protons are one of the fundamental constituents of all atoms . Protons, in addition to neutrons, are found in a very concentrated region of space within atoms referred to as the nucleus. The discovery of the proton, neutron , and electron revolutionized the way scientists viewed the atom. Recent research has shown that protons are themselves made up of even smaller particles called quarks and gluons.


Discovery and properties

Prior to the late nineteenth and early twentieth centuries, scientists believed that atoms were indivisible. Work by many scientists led to the nuclear model of the atom, in which protons, neutrons, and electrons make up individual atoms. Protons and neutrons are found in the nucleus, while electrons are found in a much greater volume around the nucleus. The nucleus represents less than 1% of the atom's total volume.

The proton's mass and charge have both been determined. The mass is 1.673 × 10-24 g. The charge of a proton is positive, and is assigned a value of +1. The electron has a –1 charge, and is about 2,000 times lighter than a proton. In neutral atoms, the number of protons and electrons are equal.

The number of protons (also referred to as the atomic number ) determines the chemical identity of an atom. Each element in the periodic table has a unique number of protons in its nucleus. The chemical behavior of individual elements largely depends, however, on the electrons in that element. Chemical reactions involve changes in the arrangements of electrons, not in the number of protons or neutrons.

The processes involving changes in the number of protons are referred to as nuclear reactions. In essence, a nuclear reaction is the transformation of one element into another. Certain elements—both natural and artificially made—are by their nature unstable, and spontaneously break down into lighter elements, releasing energy in the process. This process is referred to as radioactivity. Nuclear power is generated by just such a process.


Inner structure

Research has shown the proton to be made up of even smaller constituent particles. A proton is found to consist of two "up" quarks, each with a +2/3 electric charge , and one "down" quark, with a -1/3 electric charge. The individual quarks are held together by particles called gluons. The up and down quarks are currently believed to be two of the three fundamental particles of all matter. Recent research has revealed the possibility of an even deeper substructure, and further work could lead to new theories which may overturn the current model of the proton's structure.

See also Subatomic particles.


Resources

books

Baeyer, Hans Christian von. Rainbows, Snowflakes andQuarks. New York: Random House, 1984.

Rothman, Tony. Instant Physics. New York: Fawcett Columbine, 1995.

Trefil, James. From Atoms to Quarks. New York: Doubleday, 1980.


periodicals

Hellemans, Alexander. "Searching for the Spin of the Proton." Science 267 (March 1995): 1767.

Peterson, Ivars. "The Stuff of Protons." Science News 146 (27 August 1994): 140-41.


Michael G. Roepel

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Atomic number

—The number of protons in the nucleus of an atom.

Gluons

—Subatomic particles that help to keep quarks bound together.

Quarks

—Believed to be the most fundamental units of protons and neutrons.

Radioactivity

—Spontaneous release of subatomic particles or gamma rays by unstable atoms as their nuclei decay.

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