Answer:
Nuclear fission is the reaction in which the nucleus of a heavy atom, by capturing an incident neutron, is divided into two or more nuclei of lighter atoms, called fission products, emitting in the process neutrons, gamma rays and large quantities of energy
Explanation:
The reason why a uranium atom 235 is used in nuclear fission reactors, and not another isotope of this element or any other chemical element, is that by bombarding its nucleus with a neutron (a process known as fission induced) uranium 235 is transformed into uranium 236, which is an unstable element. This simply means that uranium 236 cannot remain long in its current state, so it is divided into two nuclei, one of barium 144 and another of krypton 89, and also emits two or three neutrons.
And here comes the really interesting thing: the sum of the masses of the barium nuclei 144 and krypton 89 is slightly less than that of the uranium core 236 from which they come ("disappears" about 0.1% of the original mass). Where has the mass we need gone? There is only one answer: it has been transformed into energy. The formula E = m c2, probably the most popular in the history of physics, relates mass and energy, and what it says is simply that a certain amount of mass equals a specific amount of energy, even though the mass is at rest.
Understanding with some precision the relationship between mass and energy is important because it helps us understand how it is possible that a mass as small as that of an atom allows us to obtain such a large amount of energy. In any case, the nuclear fission process does not end here. And it is that each of the neutrons that we have obtained as a result of the decomposition of the uranium nucleus 236 in the barium nuclei 144 and krypton 89 can interact with other fissile nuclei, causing a chain reaction.
However, not all neutrons emitted during the decomposition of uranium nucleus 236 will interact with a fissile nucleus. But it is not necessary. It is enough that only one of these neutrons does so that we obtain a stable number of fissions, and, therefore, a controlled reaction, which is the objective of the nuclear power plant reactors.
