# Nuclear Stability (Nuclear force)

In a nucleus, protons are held together in small volume, and hence they are acted upon by a large electrostatic repulsive force.

The nucleons within a nucleus are held together due to an attractive nuclear force. It is an attractive force irrespective of the nature of charges on the particles.

This force comes into play when distance between two nucleus is of the order of 10-14 m. At these distances, the nuclear force is 50 to 60 times greater than electrostatic forces.

If the radii of nuclei are plotted as a function of their mass number, it is observed that the radius increases

r = r0 A1/3 where r0 = 1.1 fm

Radius of a nucleus increases and hence the nuclear force decreases (As it is a very short range force).

It is also observed that for stable nuclei, the neutron to proton ratio (N/Z) satisfies the empirical relation:

1 ≤ N/Z < 1.6

Here, N = number of neutrons, Z = atomic number

If the number of neutrons is greater than the number of protons in a nucleus and also if N/Z > 1.6 , then the nucleus is usually unstable.

Nuclear reaction

Neutrons, in their free state are unstable particles. They decay to form a proton, an electron and an antineutrino.

* The atomic number of a neutron is zero. (Since it is neutral).

* The atomic number of a proton is 1.

* The atomic number of a β-particle is -1. (since it carries 1 unit or negative charge)