42.3 The Strong Force
Rutherford’s discovery of the atomic nucleus was not immediately accepted by all scientists. Their primary objection was that the protons would blow themselves apart at tremendously high speeds due to the extremely large electrostatic forces between them at a separation of a few femtometers. No known force could hold the nucleus together.
It soon became clear that a previously unknown force of nature operates within the nucleus to hold the nucleons together. This new force had to be stronger than the repulsive electrostatic force; hence it was named the strong force. It is also called the nuclear force.
The strong force has four important properties:
It is an attractive force between any two nucleons.
It does not act on electrons.
It is a short-range force, acting only over nuclear distances.
Over the range where it acts, it is stronger than the electrostatic force that tries to push two protons apart.
The fact that the strong force is short-range, in contrast to the long-range electric, magnetic, and gravitational forces, is apparent from the fact that we see no evidence for nuclear forces outside the nucleus.
FIGURE 42.7 summarizes the three interactions that take place within the nucleus. Whether the strong force between two protons is the same strength as the force between two neutrons or between a proton and a neutron is an important question that can be answered experimentally. The primary means of investigating the strong force is to accelerate a proton to very high speed, using a cyclotron or some other particle accelerator, then to study how the proton is scattered by various target materials.
FIGURE 42.7 The strong force is the same between any two nucleons.
The conclusion of many decades of research is that the strong force between two nucleons is independent of whether they are protons or neutrons. Charge is the basis for electromagnetic interactions, but it is of no relevance to the strong force. Protons and neutrons are identical as far as nuclear forces are concerned.