STRENGTH FUNCTIONS AND SPREADING WIDTHS OF SIMPLE SHELL-MODEL CONFIGURATIONS

The exact solution of the many-body problem in the framework of the nu clear shell model with a realistic residual Hamiltonian makes it possi ble to study the fragmentation of simple configurations as a function of excitation energy and interaction strength. The analysis is perform ed for 839 states with quantum numbers J pi T = 0(+)0 in a system of 1 2 valence particles within the sd shell. Our statistics allow us to es tablish the generic shape of the strength function in the region of st rong mixing. For the realistic interaction, the strength function is c lose to Gaussian in the central part and has exponential wings. The sp reading width is larger than predicted by the standard golden rule. At the artificially suppressed interaction strength, we recover the Brei t-Wigner shape and the golden rule for the spreading width. The transi tion between these regimes agrees with theoretical considerations base d on the idea of chaotic dynamics.