  Mixing of the shell model (SM) eigenstates due to the coupling via the common
decay channel leads in many cases to the formation of a collective eigenstate
which carries many features of the nearby decay channel. This generic mechanism
in open quantum systems explains the phenomenological Ikeda diagram and
generalizes it for various clusters/correlations in the vicinity of the
respective cluster decay thresholds. The near-threshold collectivization of the
SM states may also influence their electromagnetic decays. We discuss this
phenomenon on the example of B(EL) decays of near-threshold 2+ states in 14C.

Nuclear Theory