Answer:
Both nuclear fission and nuclear fusion are nuclear reactions that release the energy stored in the nucleus of an atom. But there are important differences between the two. Nuclear fission is the separation of a heavy nucleus into smaller nuclei, while nuclear fusion is the combination of light nuclei to create a larger and heavier nucleus.
-Nuclear fission is a reaction in which a heavy nucleus, when bombarded with neutrons, becomes unstable and decomposes into two nuclei, whose masses are of the same order of magnitude, and whose sum is slightly less than the mass of the heavy nucleus, which causes a great release of energy and the emission of two or three neutrons.
These neutrons, in turn, can cause more fission by interacting with other fissionable nuclei that will emit new neutrons, and so on. This multiplier effect is known as chain reaction. In a small fraction of time, the fissured nuclei release an energy one million times greater than that obtained, for example, in the combustion reaction of a fossil fuel.
-Nuclear fusion is a reaction in which two very light nuclei join to form a heavier, stable nucleus, with a mass slightly less than the sum of the masses of the initial nuclei. This mass defect results in a large release of energy. The energy produced by the Sun has this origin.
For fusion to take place, the positively charged nuclei must be approximated by overcoming the electrostatic repulsion forces. On Earth, where the great pressure that exists inside the Sun can not be reached, the energy necessary for the reactive nuclei to overcome the interactions can be supplied in the form of thermal energy or using a particle accelerator.
