Doorway States and the Super-Radiant Mechanism in Nuclear Reactions

In the early 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 are coupled through their common radiation field. This indirect interaction through the continuum leads to a redistribution of lifetimes among unstable intrinsic states. A rapidly decaying SR state is created at the expense of the rest of the states of the system that are robbed of their decay probability and become narrow. This mechanism is general and analogous phenomena should appear in many quantum systems when quasi-bound states are strongly coupled through common decay channels. Recently this mechanism was considered for generating doorway states in low-energy nuclear reactions. A discussion of the conditions for appearance of doorways in nuclear physics processes will is presented.