In the theory of nuclear reactions, a model in which a reaction is divided into two stages, with the first being the formation of a compound nucleus from the reactants of the reaction and the second being the disintegration of this nucleus into the products of the reaction. The model was devised by Niels Bohr in 1936. Bohr subsequently combined the compound nucleus model with the liquid drop model. The compound nucleus model has successfully described many nuclear reactions, such as neutron-induced fission, but does not describe all such reactions. A more general theory of nuclear reactions is the cloudy crystal ball model.