1. Binding Energy Per Nucleon The binding energy per nucleon of a nucleus is the binding energy divided by the total number of nucleons in the nucleus Binding energy per nucleon = total binding energy of nucleus __________________________ number of nucleons in the nucleus In the case of helium 28.3 7.1 MeV ________ = 4 The great of nuclides have a value of around 8MeV per nucleon

3. The largest value occurs at around Fe-56. This implies that Fe-56 is the most stable nucleus. Notice that uranium 235 a more massive nucleus has a lower binding energy per nucleon. If you can “split” a nucleus of U-235 you will release the excess binding energy, because lower mass “fission products” with higher binding energy per nucleon will be produced. This releases a tiny amount of energy per fission (less than 1 MeV) but this adds up to 18.7 million kWh per kg of U-235.)

4. The key to this release is the chain reaction produced by the free neutrons realesed during fission when the mass of U-235 exceeds a critical level (about 52kg- a sphere17cm in diameter

5. Less massive nuclei can relase binding energy if they are fused together to make larger nuclei. Nuclear Fusion powers the Sun where hydrogen nuclei are converted into helium atoms in a step by step process known as the proton-proton chain