IB Physics E3 Notes

Remember that the strong nuclear force is essential to the existence of nuclei, as it overpowers the charge repulsion of protons to bind them together into one cohesive mass with neutrons. However, it is only tangible up to 2.0 fm, and its effect rapidly drops off after this. Like the other fundamental forces, you are expected to know the evidence behind this force. There are two fundamental pieces of evidence you need to be aware of:

1. Nuclear binding energy – just as intermolecular forces, the creation of bonds releases energy whereas the breaking of bonds requires energy. The mass defect of nuclei is explained by the nuclear binding energy, which can only be caused by a bond between nucleons – the strong nuclear force.
2. Rutherford scattering formula – this determines the scattered intensity due to electrostatic repulsion based on the energy of the fired alpha particles. However, high energy alpha particles deviate from this formula as they close in on the nucleus and are affected by the strong nuclear force, significantly decreasing the scattering intensity.