The nuclear force is responsible for binding protons and neutrons into atomic nuclei. It is powerfully attractive between nucleons at distances around 1 femtometer but rapidly decreases beyond 2.5 femtometers. At very short distances less than 0.7 femtometers, the nuclear force becomes repulsive. The nuclear force is mediated by the exchange of pi mesons between the pion clouds that surround the quark cores of protons and neutrons.

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2. Why protons do not repel each
other in the nucleus of an atom ?

3. Nuclear force
The nuclear force (or nucleon–nucleon interaction or
residual strong force) is the force between two or more
nucleons. It is responsible for binding of protons and
neutrons into atomic nuclei.

4. Nuclear force-distances
The force is powerfully attractive
between nucleons at distances of about
1 femtometer (fm) between their centers
It rapidly decreases to insignificance at
distances beyond about 2.5 fm.
At very short distances less than 0.7 fm,
it becomes repulsive.

5. Interaction of nucleons through pion.

6. The model above shows a proton and neutron with overlapping pion fields,
allowing the proton to donate a pion to the neutron, contributing to the
nuclear force holding the two nucleons together.

7. Nuclear Core structure
 The core of the nucleon which is surrounded by the pion cloud consists
of particles called quarks.
 Quarks come in different types.
 The proton and neutron are composed of three quarks of two different
types.
The proton is composed of two up-quarks and one down-quark and so
can be written: uud.
The neutron is composed of one up-quark and two down-quarks and so
can be written udd.

8. Interaction of nucleons mediated by
pion-quark constituents.