AS AQA Phys Unit 1- Stable and Unstable Nuclei

Strong Nuclear Force

Several different forces act on the nucleons in the nucleus. There are the electrostatic forces, due to the charges on protons and there are gravitational forces, due to the masses of the particles.

The repulsion from the electrostatic force (between two protons) is much greater than the gravitational attraction. Therefore another force is needed to hold the nucleus together, this is the strong nuclear force;

The strong nuclear force keeps isotopes stable. It overcomes the electrostatic force of repulsion and (except in unstable nuclei) keeps the protons and neutrons together.

1) To hold the nucleus together it must be an attractive force, stronger than the electrostatic force.

2) It has a very short range, so can only hold nucleons together when they're seperated by up to a few femtometres - the size of a nucleus.

3) The strength of the strong nuclear force quickly falls beyond this distance.

4) Experiments also show the strong nuclear force works equally between all nucleons. This means size of force is the same whether it's between proton-proton, neutron-neutron or proton-neutron.

5) At very small seperations, the strong nuclear force must be repulsive- otherwise the nucleus would 'crush' to a point.

Varying size

The size of the strong nuclear force varies with nucleon seperation. When compared against electrostatic repulsive force on a graph;

• The strong…