1. Binding Energy
Nucleons (neutrons and protons) are bound together in the nucleus, and so it costs energy to tare the nucleus appart. Reversely, energy must therefore be gained by assembling the nucleus. Where does this energy come from? It comes from the mass of the protons and neutrons.

2. Binding Energy
The energy that is needed to tare the nucleus apart is called the binding energy EB. The binding energy stems from the difference between the mass of the nucleus and the mass of the free nucleons. This mass difference is called the mass defect Δm:
EB = Δm.c2
Take a look at table B3 on page 98.
Exercise: The mass of Lithium-6 is kg. Calculate the binding energy.

3. Binding Energy per Nucleon

4. Fission
For heavy elements, energy may be gained, if the nucleus splits into two or more fragments. This is called fission. This is what happens in a nuclear power plant. The energy gain stems from the difference in the mass of the mother nucleus and the daughter nuclei (see. P. 99).

5. Nuclear Power Plants
The heat from the fission process heats the water that drives a turbine.

6. Fusion
For light elements, energy may be gained, if two nuclei fuse. This is called fusion. This is what happens in the Sun.
The energy gain stems from the difference in the mass of the mother nucleus and the daughter nuclei (see. P. 104).