Proton in Quantum Physics by mypersonalcafe


									A proton is a positively charge particle that resides within the atomic
nucleus. The number of protons in the atomic nucleus is what determines
the atomic number of an element, as outlined in the periodic table of the
The proton has charge +1 (or, alternately, 1.602 x 10-19 Coulombs), the
exact opposite of the -1 charge contained by the electron. In mass,
however, there is no contest - the proton's mass is approximately 1,836
times that of an electron.

A proton is a subatomic particle found in the nucleus of all conventional
atoms. The only place you can find matter without protons is in a neutron
star or the core of powerful particle accelerators. The proton has a
positive charge, which balances out the negative charge in atoms,
electrons. If an atom has an imbalance of protons or neutrons, it is no
longer neutral and becomes a charged particle, also known as an ion.

It is difficult to determine who, exactly, discovered the proton.
Scientists theorized the existence of positively charged particles after
the discovery of the electron by J. J. Thomson in 1897. Ernest Rutherford
is often credited with the discovery, however, based on his experiments
in 1918.

Rutherford fired alpha particles, which are essentially helium nuclei
without electrons, into a nitrogen gas. His detectors found the
characteristic signature of hydrogen nuclei being produced. After
thinking about it for a while, he realized that these hydrogen nuclei
could have only come from the nitrogen gas. This led to the theory that
the nucleus of a hydrogen atom was an elementary particle, the proton,
and that protons could be found in the nuclei of all atoms.

The properties of atoms are defined by the number of electrons, neutrons
and protons they have. The number of protons is the most significant
variable, however. This variable is so significant, in fact, that the
number of protons in the nucleus of an atom is referred to as the atomic
number, and atoms are named based on the number of protons they have.

The atomic number is the most physically relevant characteristic of an
atom. Atoms with low atomic numbers are the most prevalent in the
universe, because they are the easiest to form. This is why hydrogen and
helium are the most abundant elements in the universe.

In 1955, the proton's evil twin, the antiproton, was discovered. Instead
of having a positive charge, it has a negative one. Like all antimatter,
it explodes upon contact with normal matter.

Protons are also a favorite among experimental physicists who like to
accelerate them to significant fractions of the speed of light. Ballistic
protons are responsible for a lot of discoveries in the huge "Particle
Zoo" that 20th century physics generated. Unlike their cousins, neutrons,
protons are stable outside of an atomic nucleus, making them useful for
purposes of experimentation.

Discovery of the Proton
The proton was discovered by Ernest Rutherford in 1918 (though the
concept had been earlier suggested by the work of Eugene Goldstein). The
proton was long believed to be an elementary particle until the discovery
of quarks. In the quark model, it is now understood that the proton is
comprised of two up quarks and one down quark, mediated by gluons in the
Standard Model of quantum physics.

Proton Details

Since the proton is in the atomic nucleus, it is a nucleon. Since it has
a spin of -1/2, it is a fermion. Since it is composed of three quarks, it
is a triquark baryon, a type of hadron. (As should be clear at this
point, physicists really enjoy making categories for particles.)

Mass: 938 MeV/c2 = 1.67 x 10-27 kg
Charge: +1 fundamental unit = 1.602 x 10-19 Coulombs
Diameter: 1.65 x 10-15 m

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