 The way that this extra energy is typically provided is to make a target out of isotopically enriched water and bombard it with a beam of energetic protons from a particle accelerator. The reason for the isotopically enriched water is because the chemical symbol of water is H2O, but most natural oxygen atoms are Oxygen 16, with only a very small fraction of Oxygen 17 and Oxygen 18. It is possible, however, to preferentially select Oxygen 18 atoms and hence create water where the Oxygen component is essentially all Oxygen 18. If we look at the difference in the masses of the products and the reactants, we can see that 2.44 MeV of energy must be put into the system to initiate the nuclear reaction. However, it turns out that higher energies of around 18 MeV are usually used and many hospitals have a small accelerator called a cyclotron that can be used to initiate this and other nuclear reactions by heating atoms with energetic beams of other nuclei. Another example of an artificially induced nuclear reaction is neutron-induced fission of Uranium-235. When a neutron combines with the Uranium-235 nucleus, the resulting nucleus, Uranium-236, is in an excited state that can easily split in two. It turns out to be energetically favourable for the nucleus to break up, typically making two products with mass numbers around 100 to 145 and 90 to 95, as well as 2 to 3 neutrons. One of the most common set of products that can be created is given here as an example. Again, we can look at the masses in atomic mass units and look at how the masses change. In this particular case, the mass of the products is 0.19279 atomic mass units less than the mass of the reactants. This corresponds to approximately 180 MeV of energy being emitted in the reaction. This energy is primarily released in the form of kinetic energy of the products. The very large energy released from this process is the basis of a nuclear fission reactor and this will be discussed in detail in the next lecture.