Reactor Bin: Fusion

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Fusion - The Reaction

If you add up the masses of the particles which go into a fusion reaction, and you add up the masses of the particles remaining, there is frequently a difference. According to Einstein's famous law relating energy and mass, E=mc², the "mass difference" can take the form of energy. Fusion reactions involving nuclei lighter than iron typically release energy, but fusion reactions involving nuclei heavier than iron typically absorb energy. The amount of energy released depends on the specifics of the reaction.

Another way to look at this is to consider the bonding energy of the elements in question. If the reactants are bound more weakly than the products, then energy is released in the reaction. Bonding energy is the amount of energy you would have to put into a system in order to pull its components apart; conversely, in a system with high bonding energy, a large amount of energy is released as the components are allowed to bond together. Suppose you had two balls connected by a long, thin rubberband, so that they are not very tightly connected, and the rubberband can be broken easily. This is a system with low binding energy.

While it is possible to take any two nuclei and get them to fuse, it is easiest to get lighter nuclei to fuse, because their charge is not as strong, and therefore easier to squeeze together. There are complicated quantum-mechanics rules which determine what products you will get from a given reaction, and in what amounts (branching ratios). The probability that two nuclei will fuse is determined by the physics of the collsion, and a property called the cross section Which (roughly speaking) measures the likelihood of a fusion reaction.

What's cold fusion? --)