1. Nuclear Fission
Elliott

2. Fission Large nuclei have a lower binding energy per nucleon.
This means that they are less stable.  
This lack of stability is usually shown by radioactive decay, which occurs in a predictable way.  
Very rarely a large nucleus will split up spontaneously into fragments.  This splitting of the nucleus is called fission.

3. Wobbly Drop
The easiest way to explain this is to consider the nucleus as a “wobbly drop”.  
Nuclei are not tidy and neatly arranged rows of neutrons and protons; they are microscopic bedlam. 

4. The strong nuclear force acts between neighbouring nucleons
The strong nuclear force acts between neighbouring nucleons. The nucleons are not linked with the same neighbours all the time.  
However the enough of the nucleons linked to stop the repulsive electromagnetic force tearing the nucleus apart.

5. Uranium 235
We can induce fission in large nuclei such as uranium-235.  The most common isotope of uranium, U-238, does not split easily, but the 235 isotope does.  
We induce fission by “tickling” the nucleus with a “thermal” neutron.  
The neutron has to have the right kinetic energy:
Too little kinetic energy means that the neutron will bounce off the nucleus;
Too much kinetic energy means that the neutron will go right through the nucleus.
Just right means that the neutron will be captured by the strong force, which is attractive between nucleons.  The neutron gives the nucleus enough energy to resonate.

6. Dr. D Ross
Chain Reaction
The tickled nucleus flies apart into a number of fragments, leaving on average three neutrons left over. These too are able to tickle other nuclei and make them split. Each neutron spawns three more neutrons in each fission, so we get a chain reaction.
There is a mass defect in the products of the fission so energy is given out.   In an uncontrolled chain reaction, the energy is given out in the form of a violent explosion.

7. Check Your Progress
A thermal neutron is one that has a kinetic energy of about 1 eV.  How fast does a thermal neutron travel?

8. Answer

9. Fusion Fusion means joining nuclei together. Very difficult to do.
The idea is that light nuclei are joined together, increasing the binding energy per nucleon.
This will result in lots of energy being given out.

10. Conditions Required Each nucleus has to have sufficient energy to:
Overcome electrostatic repulsion from the protons;
Overcome the repulsive strong force which is found outside the region of the strong force.
This means that the gases have to be heated to a very high temperature, 100 million Kelvin.  As all matter at this temperature exists as an ionised gas (plasma), it has to be confined in a very small space by powerful magnetic fields
A fusion reactor would be made to boil water to turn a turbine.  Fusion has occurred, but the energy put in to cook the gases enough to make them fuse is far greater than the energy got out by a fusion reaction.

11. Advantages of Fusion over Fission
Fusion, if it could be made to work, has a number of advantages over fission:
Greater power per kilogram of fuel used;
Raw materials are cheap and readily available
No radioactive elements are made by the reaction.

12. Check Your Progress
Data to use: Mass of deuterium nucleus = × kg Mass of tritium nucleus = × kg Mass of helium nucleus = ×10-27 kg Mass of a neutron = × kg What is the energy in J and eV released in this reaction above?

13. Answer