  The chaotic mixing by random two-body interactions of many-electron Fock
states in a confined geometry is investigated numerically and compared with
analytical predictions. Two distinct regimes are found in the dependence of the
inverse participation ratio in Fock space I on the dimensionless conductance of
the quantum dot g and the excitation energy E. In both regimes I>>1, but only
the small-g regime is described by the golden rule. The crossover region is
characterized by a maximum in a scaling function that becomes more pronounced
with increasing excitation energy. The scaling parameter that governs the
transition is (E/g)ln g.
