Proton, The Charged Nucleon
The proton, the nucleus of the Hydrogen atom and the building block of all nuclear charge,
has a mass of about 0.938 GeV/c2 or 1.67 10-27 kg and a spin angular
momentum of 1/2 unit of Planck's constant. For most of the 20th century the proton was thought
to be a point-like particle. We now know, however, that, instead of being point-like,
the proton has a radius of about 10-15 meter and that it is a complex dynamical
system consisting of three "quarks".
The dynamics of this bound system are still imperfectly
understood but it is well-established that the underlying theory
is the SU(3) gauge theory now known as "quantum chromodynamics".
This theory of the
was proposed by
Macedonian translation of this web page (by Web Geek Science)
The proton is a color
neutral combination of
three colored quarks
(one of each color).
The quarks are
by the exchange
of color gluons. The
emission or absorption
of a gluon causes the quarks
to make a transition from one
color to another.
Unlike the simplified animation
presented here, the gluons are
associated with two colors,
that of the emitting quark and that of the receiving quark.
"Color" in this context is used to specify a property of quarks having
three possible values and is not meant to be taken in the literal sense
of color as it appears to the human eye.
Nambu's original motivation for proposing the theory was the observation that such a
force would guarantee that the lowest mass states were color "neutral". It is now
thought, in fact, that non-color-neutral hadrons would have infinite mass.
In the proton, two of the quarks are of 'up' type flavor while the third is 'down' type.
The neutron (neutral nucleon) is identical to the proton except it has two 'down' type
and one 'up' type quark.
In the most advanced theories, the quarks and gluons are string-like rather than
pointlike. Experimentally, we know only that the spatial extent of quarks and gluons is
less than about 10^(-18) m, i.e. less than 1/1000 the radius of the proton.