Doorway states, the super-radiant mechanism and nuclear reactions

In the 1950s the possibility of forming a "super-radiant" (SR) state in a gas of atoms confined to a volume of a size smaller than the wave length of radiation was suggested by Dicke. The atoms, with two levels, are coupled through their common radiation field. This indirect coupling leads to a redistribution of lifetimes among unstable intrinsic states. A strongly decaying SR state is created at the expense of the rest of the states of the system. Recently the connection of this mechanism to the notion of doorway states in low-energy nuclear reactions, was pointed out. The conditions for appearance of such doorways in nuclear physics processes are discussed.