Where the Energy Comes from

These simple examples are of course far removed from plutonium, uranium, huge reactors and atom bombs. They illustrate however the principle that it is possible to artificially transform elements. We are approaching now the great Uranium fission reaction which is far more complex than these simple examples. But before this there is one other important question we have so far ignored which must be answered. So these reactions can take place, how is it possible to get energy out of them?

The release of energy from nuclear reactions can be shown in another innocuous, but historic example. In 1932 the following reaction was produced: Lithium 7 was bombarded with Hydrogen 1, the product of the reaction was two Helium 4 atoms. When measuring weights, it is hopelessly impractical to use grams, milligrams or even micrograms. The unit of mass that is used is the Atomic Mass Unit (amu). The mass of a proton is a approximately 1 amu.

If we measure the weights of the reactants (in amu's) they are 7.016004 for lithium and 1.007825 for hydrogen giving a total of 8.023 amu. The mass of helium however is 4.002603 amu. So the mass of the products of the nuclear conversion is 8.005206 amu. This means that in the course of the reaction 0.018623 amu of mass is "lost". Actually "lost" is not the correct term, it is in fact converted to energy. The amount of energy being given by Einstein's famous equation: (Energy released) = (mass lost) × (speed of light) × (speed of light).

Well how much energy is this? If we apply Einstein's equation (and convert to units we are more familiar with) it turns out that one Lithium atom being hit by a hydrogen atom will produce, if it happens once a second. 0.0000000000028 watts. Not very much power at all! However in one gram of Lithium there are 6,024,000,000,000,000,000,000,000 atoms. So if one gram of lithium were converted per second, it would produce 1,674,394,000 kw. Quite a bit of power!

Well, you may ask, how is this energy released? The answer depends really on how big you are. If we were about the same size as atoms, we would see two helium atoms moving around more rapidly than were the original lithium and hydrogen atoms. Being, however somewhat larger, we are not able to observe this. What we detect is the consequence of particles moving more rapidly - we feel the container get hotter. Temperature is nothing more than the speed with which the mole— cules or atoms are vibrating or moving around in the substance.