Spark image
Binding energy

If you take two protons and two neutrons, measure their masses, make them stick them together somehow and then measure the mass of the finished helium nucleus. You will find that the mass of the completed nucleus is less than the total mass of the four particles.

This can best be explained by looking at how easy it would be to split the nucleus again. Think of this mass difference as a difference of energy. This difference in mass is called the mass defect of the nucleus.The helium nucleus has 28.3 MeV less energy than the four particles. It means that this energy would be needed to split up the helium nucleus. This is called the binding energy of a nucleus.

The mass defect for a number of nuclei is shown below.

12 Carbon 6 0.099 00
16 Oxygen 8 0.137 08
40 Calcium 20 0.367 41
56 Iron 26 0.528 75
208 Lead 82 1.757 84
235 Uranium 92 1.935 38
 
 
© Keith Gibbs