Nuclear Force

Inside the atom, electrons are held by electrostatic attraction, but the nucleus contains positively charged protons packed into a very small space. Since protons repel one another, a much stronger attractive force must exist to hold the nucleus together.

The nuclear force is the strong attractive force between nucleons (protons and neutrons) that binds them together inside the nucleus.

• The binding energy per nucleon in nuclei is about 8 MeV, which is far larger than the binding energy per nucleon in ordinary atoms. 
• Therefore, the force that binds nucleons cannot be the same as the force responsible for ordinary atomic structure. 
• This special attractive force acting between nucleons is called the nuclear force.
• It acts between proton-proton, neutron-neutron, and proton-neutron pairs. 
• It is effective only over very small distances inside the nucleus. 
• It is responsible for the stability of nuclei. 

Very Strong Force

• The nuclear force is much stronger than the gravitational force.
• Inside the nucleus, the strong force is strong enough to overcome the electrostatic repulsion between protons.
• This is why nucleons can remain bound within a tiny nuclear volume.

Short-Range Force

• The nuclear force acts only over a very short distance.
• Its effect falls rapidly to zero beyond a few femtometres.
• Because of this short range, a nucleon mainly interacts with its nearby nucleons.

Saturation Property

• Since each nucleon interacts strongly only with neighbouring nucleons, the nuclear force shows saturation.
• This explains why the binding energy per nucleon remains nearly constant for many medium and heavy nuclei.

Charge Independence

• The nuclear force is nearly the same for neutron-neutron, proton-neutron, and proton-proton pairs.
• Therefore, it does not depend on the electric charge of the nucleons.

Repulsive at Extremely Small Distance

• The potential energy curve for two nucleons shows a minimum at about r₀ ≈ 0.8 fm.
• For separations larger than r_{0, the force is attractive, helping to} bind nucleons.
• For separations smaller than r₀, the force becomes strongly repulsive.

No Simple Mathematical Law

• Unlike Coulomb's law or Newton's law of gravitation, the nuclear force does not have a simple universal mathematical expression.