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term applying to both the protonproton,
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.
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 and the neutronneutron,
uncharged elementary particle of slightly greater mass than the proton. It was discovered by James Chadwick in 1932. The stable isotopes of all elements except hydrogen and helium contain a number of neutrons equal to or greater than the number of protons.
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, the two constituents of atomic nuclei. The nucleon may be considered a single particle, of which the proton and the neutron are two different states. See atomatom
[Gr.,=uncuttable (indivisible)], basic unit of matter; more properly, the smallest unit of a chemical element having the properties of that element. Structure of the Atom
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; elementary particleselementary particles,
the most basic physical constituents of the universe. Basic Constituents of Matter

Molecules are built up from the atom, which is the basic unit of any chemical element. The atom in turn is made from the proton, neutron, and electron.
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The collective name for a proton or a neutron. These subatomic particles are the principal constituents of atomic nuclei and therefore of most matter in the universe. The proton and neutron share many characteristics. They have the same intrinsic spin, nearly the same mass, and similar interactions with other subatomic particles, and they can transform into one another by means of the weak interactions. Hence it is often useful to view them as two different states or configurations of the same particle, the nucleon. Nucleons are small compared to atomic dimensions and relatively heavy. Their characteristic size is of order 1/10,000 the size of a typical atom, and their mass is of order 2000 times the mass of the electron.

The proton and neutron differ chiefly in their electromagnetic properties. The proton has electric charge +1, the opposite of the electron, while the neutron is electrically neutral. They have significantly different intrinsic magnetic moments. Because the neutron is slightly heavier than the proton, roughly 1 part in 1000, the neutron is unstable, decaying into a proton, an electron, and an antineutrino with a characteristic lifetime of approximately 900 s. Although some unified field theories predict that the proton is unstable, no experiment has detected proton decay.

The complex forces between nucleons and the discovery during the 1950s of many similar subatomic particles led physicists to suggest that nucleons might not be fundamental particles. During the late 1960s and 1970s, inelastic electron and neutrino scattering experiments indicated that nucleons are composed of pointlike particles with spin ½ and electric charges that are fractions of the charge on the electron. Particles with similar properties, named quarks, had been hypothesized in the early 1960s to explain other regularities among the properties of hadrons. In the early 1970s, it became clear that nucleons and other hadrons are indeed bound states of quarks. See Hadron, Nuclear structure

Quarks are believed to be fundamental particles without internal structure. The proton consists of two up-type quarks and one down-type quark (uud), while the neutron consists of ddu. Quarks are bound into nucleons by strong forces carried by gluons. The nucleon contains ambient gluon fields in somewhat the same way that the atom contains ambient electromagnetic fields. Because quarks and gluons are much less massive than the nucleon itself, their motion inside the nucleon is relativistic, making quark-antiquark pair creation a significant factor. Thus the nucleon contains fluctuating quark-antiquark pairs in addition to quarks and gluons. The theory of quark-gluon interactions is known as quantum chromodynamics (QCD), in analogy to the quantum theory of electrodynamics (QED). See Elementary particle, Gluons, Neutron, Proton, Quantum chromodynamics, Quantum electrodynamics, Quarks


(new -klee-on) One of the constituents of the atomic nucleus, i.e. a proton or a neutron.


A collective name for a proton or a neutron; these particles are the main constituents of atomic nuclei, have approximately the same mass, have a spin of ½, and can transform into each other through the process of beta decay.


a proton or neutron, esp one present in an atomic nucleus
References in periodicals archive ?
The nucleons in the core of the nucleus undergo only the interaction with their closest neighbors.
Since we are dealing with a nucleon-core interaction where the nucleon mass is [m.
Let the four polarized neutrons disposed symmetrically like the nucleons in the alpha particle, as shown in the figure.
DNA from the peripheral blood cells was extracted in accordance with the Nucleon TM DNA Extraction Kit (GE Healthcare).
003) between nucleon diversity estimates and survey effort, as indicated by the average number of fragments or sites surveyed in a sampled individual (table 3); that relationship was expected on theoretical grounds (Nei 1987).
Every Type II supernova (one resulting from the core collapse of a giant star) ought to leave behind a neutron -- or nucleon -- star.
However, these outlines would fail to explain IB's at low spin, where the blocking of the pairing contributions of the odd nucleon is predicted to reduce the nuclear superfluidity, there by increasing the moment of inertia of the odd-A nucleus.
At present, we have detailed maps of the distribution of quarks and gluons in the nucleon in 1D (as a function of their momentum in a single direction).
8]) particle and the tau lepton, (17) the observation of constituent particles within a nucleon and the first measurement of the B-meson life time.
Other subjects explored are topological field theories with non-semisimple gauge group of symmetry, continuity equations in Riemannian spaces, the non-Hamiltonian nature of nucleon dynamics in an effective field theory, and singular value decomposition and Lanczos potential.