الفهرس 
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Abstract
The nucleus of an atom is the very dense region, consisting of nucleons (protons
and neutrons), at the center of the atom. Although the size of the nucleus varies
considerably with the mass of the atom, the size of the entire atom is comparatively
constant. Almost all of the mass in an atom is made up from the protons and neutrons in
the nucleus with a very small contribution from the orbiting electrons.
The diameter of the nucleus is in the range of 1.6 fm (1.6 ×10 m) (for proton
in light hydrogen) to about 15 fm (for the heaviest atoms, such as uranium). These
dimensions are much smaller than the size of the atom itself by a factor of about 23,000
(uranium) to about 145,000 (hydrogen).
The nucleus of an atom consists of protons and neutrons (two types of baryons)
bound by the nuclear force (also knowing as the residual strong force). These baryons are
further composed of subatomic fundamental particles known as quarks bound by the strong
interaction. Which chemical element an atom represents, is determined by the number of
protons in the nucleus .Each proton carries a single positive charge, and the total electrical
charge of the nucleus is spread fairly uniformly throughout its body, with the exception of
hydrogen and helium, where the charge is concentrated near its core. As each proton
carries a unit of charge, the charge distribution is indicative of the proton distribution, and
the neutron distribution probably is similar.
The branch of physics concerned with studying and understanding the atomic
nucleus, including its composition and nuclear forces which bind it together, is called
nuclear physics. Its applications go from nuclear weapons to the use of radioisotopes. It
also forms the basis of understanding how the stars generate energy and about how the
elements were created.