A unified model of preequilibrium decay

A microscopic exciton model has been developed which describes the time evolution of a highly excited nucleus through a series of binary collisions creating additional particle-hole pairs. Starting from an arbitrary exciton density distribution, the spectral shapes of the succeeding stages are generated through recursion relations which keep track of the “exciton flux” explicitely. The computer code BEEFALO provides particle spectra and average life times of the successive stages. The results are compared with the predictions of other preequilibrium models using “equal probability” density distributions. The controversy about the use of single particle orn-exciton state life times has been resolved by showing that both approaches lead to the same particle spectra if proper book-keeping is made through appropriate recursion relations.