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Proton

2007 Schools Wikipedia Selection. Related subjects: General Physics

                                                              Proton
                                                          Classification


                             Subatomic particle
                                  Fermion
                                   Hadron
                                   Baryon
                                  Nucleon
                                   Proton

                                                           Properties


                                  Mass:       1.672 621 71(29) × 10^−27 kg
                                                938.272 029(80) MeV/c^2
                             Electric Charge: 1.602 176 53(14) × 10^−19 C
                                 Radius:           about 0.8×10^−15 m
                                  Spin:                    ½
                                  Quark
                               Composition:           1 down, 2 up

   In physics, the proton ( Greek πρῶτον proton = first) is a subatomic
   particle with an electric charge of one positive fundamental unit
   (1.602 × 10^−19 coulomb), a diameter of about 1.5×10^−15 m, and a mass
   of 938.3 MeV/c^2 ( 1.6726 × 10^−27 kg), or about 1836 times the mass of
   an electron. The proton is observed to be stable, although some
   theories predict that the proton may decay. The proton has a density of
   about 2.31 × 10^17 kg m^−3.

   Protons are spin-1/2 fermions and are composed of three quarks, making
   them baryons. The two up quarks and one down quark of the proton are
   also held together by the strong nuclear force, mediated by gluons.
   Protons may be transmuted into neutrons by inverse beta decay (that is,
   by capturing an electron); since neutrons are heavier than protons,
   this process does not occur spontaneously but only when energy is
   supplied. The proton's antimatter equivalent is the antiproton, which
   has the same magnitude charge as the proton but the opposite sign.

   Protons and neutrons are both nucleons, which may be bound by the
   nuclear force into atomic nuclei. The most common isotope of the
   hydrogen atom is a single proton. The nuclei of other atoms are
   composed of various numbers of protons and neutrons. The number of
   protons in the nucleus determines the chemical properties of the atom
   and which chemical element it is.

Antiproton

   The antiproton is the antiparticle of the proton. It was discovered in
   1955 by Emilio Segre 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 9×10^11. The magnetic moment of the antiproton has been
   measured with error of 8×10^−3 nuclear Bohr magnetons, and is found to
   be equal and opposite to that of the proton.

High-energy physics

   Due to their stability and large mass (compared to electrons), protons
   are well suited to use in particle colliders such as the Large Hadron
   Collider at CERN and the Tevatron at Fermilab. Protons also make up a
   large majority of the cosmic rays 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.

   Retrieved from " http://en.wikipedia.org/wiki/Proton"
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