Generalized Exact Spatially Dependent Neutron Slowing Down Distribution Near Source Lethargy

Exact elementary functions for the value and first two lethargy derivatives of the collided neutron flux at source lethargy have been derived previously for a monoenergetic plane source in hydrogen, and the results have been used both to test calculational methods and to synthesize an elementary function for the entire spatially dependent slowing down distribution. In this Note, the exact elementary functions at source lethargy are generalized to allow: (a) any number and thicknesses of homogeneous slabs with faces parallel to the source plane, (b) each slab to be composed of any mixture of isotopes with arbitrary energy-dependent elastic scattering and absorption cross sections, and (c) any number of equally spaced cosine-weighted source planes.