Approximated space-energy resolution of fast-neutron fluxes

Based on a polynomial approximation, the model accuracy increases with the order of the expansion. It is, in fact, a generalization to N terms of the one-term classical slowing down models such as those of Fermi, Wigner, and Greuling-Goertzel. Equivalent to the classical and synthetic expression of our Q/sub N/ model, a determination of a ''differential'' expression of the model is proposed which allows the calculation of a set of functions approximating the kernel Σ/sub s/(u' → u). To be used in reactor codes, the spectrum determination has to be associated to a spatial resolution; the adaptation of the Q/sub N/ method to the collision probability approximation or the calculation of a spatial Green's function to obtain a flux phi(r, E) is described. The applications in the isotropic collision approximation can be extended to the linearly anisotropic approximation, and various results that demonstrate the validity of the method are given