Nuclear chain reaction is a sequence of single nuclear reactions,
each of which is caused by a particle that appeared as a reaction product at
the previous step of the sequence. An example of a nuclear chain reaction is
the nuclear chain reaction of the fission of nuclei of heavy elements, in which
the majority of fission events are initiated by neutrons produced by nuclear
fission in the previous generation.
Chain reactions are widespread
among chemical reactions, where free atoms or radicals play the role of
particles with unused bonds. The mechanism of the nuclear chain reaction in
nuclear transformations can provide neutrons that do not have a Coulomb barrier
and excite the nucleus during absorption. The appearance of the necessary
particle in the medium causes a chain of the following, one after the other
reactions, which continues until the chain breaks due to the loss of the
carrier particle of the reaction.
