Nuclear Physics: Control of the Chain Reaction involved in Fission of the Uranium Nucleus

IT has recently been shown that the number 1 of neutrons liberated 2 in the nuclear fission of a uranium nucleus is sufficiently high to make the realization of a self-perpetuating reaction chain seem possible. The danger that a system containing uranium in high concentration might explode, once the chain is started, is considerable. It is therefore useful to point out a mechanism which gives the possibility of controlling the development of such a chain.