Application of the Direct Microscopic Formalism to Nuclear Data Evaluation

Abstract

We review the basic definitions of the direct microscopic formalism (DMF) and the corresponding model code TRANSNU, to describe pre-equilibrium nuclear systems, as elements of the grand canonical ensemble. We analyze its inconsistencies, especially the impossibility of exact solution of the nuclear many-body problem, and propose solutions. We use the strong dependence of pre-equilibrium emissions on the ratio of transition rates, in code ${\bf \mbox{TNG}}$, to propose a redefinition of the parameters in the master equation, and obtain smoother excitation functions in the energy regions where different exciton classes contribute. We compare the transition rates of TRANSNU with the phenomenological ones for the estimation the excitation function of a few p-induced reactions on $^{56}$Fe, and obtain reasonable descriptions for activation energy, local maxima and average magnitude. Despite the inconsistencies and a few remaining numerical problems, related with non meaningful noises in the strong oscillations of the TST, especially with the excitation energy and for low exciton number, we find the results of the present work very promising, indicating that the DFM can be used as a more precise and physically meaningful approach for the study of nuclear systems in pre-equilibrium than the traditional statistical models.